The confusion cleared with such instant clarity that it was almost disorienting in itself and Knuckles knew in an instant exactly where he was, in spite of the fact he was still spinning, tumbling in all three axes. Still falling, slick blue-green bricks whipping past. Knuckles twisted to to get air under his spines, but had only gotten himself half way round when he saw what was beneath them and changed his plan from a glide to a dive into the deep water.

There was a tremendous splash and instantly his vision was obscured by bubbles as Sonic hit the water flat on his back a second behind him and Tails plunged in after them. Knuckles let himself drift for a moment waiting for the bubbles to clear, holding his breath, orienting himself. Tails must have also held his breath at the moment of impact and was swimming, pulling at Sonic, who had either gasped or yelled and was now thrashing wildly, choking, drowning.

Tails was heaving with all his might, but Knuckles knew the surface was too far away, even without the churning undertow. He swatted Tails off, gesturing sharply at himself then Sonic. Tails blinked at him, terrified, but let go. Knuckles dragged the hedgehog further down, easily overpowering his disoriented efforts to fight back, and hoping he didn't take it into his panicked head to spindash his way free. Instead, a flailing sneaker caught Knuckles in the stomach and he lost his grip for a moment, coughing bubbles into the water and fighting the urge to curse. He tried again, struggling to contain the hedgehog's increasingly wild contortions. Blue spikes swept dangerously near his face and he snatched at the only thing he could see which wasn't sharp – grabbing hold of Sonic's right ear.

Something crunched unpleasantly under his fingers and Sonic jack-knifed in the water, but pain from such an unexpected quarter seemed to have snapped him out of panic for at least a second or two and Knuckles seized the moment to shove him the rest of the way to the bottom and force his face hard against the emergency breather vent. He was afraid it would be difficult to make Sonic breathe from it in his confusion but he'd been gasping in water so wildly that he gasped in the air with equal panicked abandon.

Knuckles hauled him off it, clamped his hand around the hedgehog's muzzle and dragged his face round until Sonic's alarmed, blinking, eye-rolling gaze was at least vaguely looking at him and indicated as best he could by mime the importance of holding his breath.

Knuckles' own breath ached in his chest as he glanced over his shoulder. Tails had got the idea and dipped down to the breather. Perhaps he'd figured them out on their previous, uninvited visit. As Tails moved away, Knuckles let go of Sonic's muzzle and pushed the hedgehog's head back down into the bubble stream. One breath, two and he pulled him back up. Sonic kept his mouth tightly shut this time, and there was only fear in his eyes, no longer blind panic despite the fact he was shivering violently in Knuckles' grip.

Or maybe it was Knuckles himself trembling he realised, because he really, really needed to breathe now. Would have needed to even without the exertion of dealing with Sonic. He was light-headed, the edges of his vision losing what little colour there was to be seen through the dark water. He shoved Sonic vaguely in Tails' direction and dived to his hands and knees over the breather vent. A gasp of a breath and then a second more controlled, deeper one and he floated aside for Tails, with his arm round Sonic, to go back in.

Knuckles tapped Tails on the shoulder as he pulled Sonic back upright. As they both looked wide eyed at him he tapped his chest – then pointed to a passageway above and to their right and back to the breather.

Hoping he'd conveyed the message that he knew a safe route, Knuckles pointed back to the breather again, tapped himself, then Tails, then Sonic. In that sequence Sonic would have had the most recent breath before they moved off.

Despite the breathers, Knuckles knew Sonic must have taken in a certain amount of water, and it was clearly costing him a lot of effort not to cough and make things worse. He set a fast pace, heading for next dry area he knew of, Tails on Sonic's other side matching him.

Navigating the tunnels and the currents was easy, almost without thought, and after less than a minute Knuckles pulled himself up out of the water and reached back for Sonic who was slumped on the top step with his knees still in the water and his upper half sprawled across the damp stone tiles, coughing and retching violently.

Tails was patting him hard on the back and Knuckles didn't really have any better ideas than that so he got to his feet and checked instead that they weren't about to be surrounded by invaders while they pulled themselves together. With his feet firmly planted back on the Island it was easy to shrug off the adrenaline weariness of the unexpected plunge and the scuffle with Sonic. Sheer relief washed out every other sensation and he leaned against the slick marble, hands pressed flat against it. He was home. Safe. And home was safe. The Master Emerald was safe. He closed his eyes and drew a long breath that felt like he'd been holding it for days.

Sonic, by contrast was breathing in sharp gasps and it was long minutes before he was able to climb the rest of the way out of the water. He made to sit down against the wall but Knuckles grabbed his arm to keep him on his feet.

"Gimme a break!" Sonic protested.

"No. Keep moving. There's rings along here, look."

Sonic looked up. "Yeah?"

Two clusters of rings later he was looking recovered enough to hesitate at the next set. "Tails? D'you need…"

Tails was already shaking his head.

"I'm good."

Sonic turned to Knuckles, looking him up and down, as if for the first time. "Well you definitely do, Knux - how did you get so scratched up?"

Knuckles looked down at himself. Sonic was right, his arms and chest were criss-crossed with shallow cuts, turning the water that still dripped from them pink.

"You weren't keen on my help and you're spikey," Knuckles summarised abruptly.

Sonic blinked at him. "Uh, yeah? Hedgehog? Wait. That was me?"

"Don't worry about it. Rings or not, that help's going to have left you a few bruises. We're probably pretty even."

Sonic rubbed the side of his face where Knuckles had rammed it against the vent and cautiously felt at his ear. "Yeah, fair enough. I won't take it personally if you don't."

Knuckles nodded minutely and stepped forward into the short line of rings in the passageway ahead, feeling the tingle as the little bursts of concentrated energy spread through him, chiming soothingly with the background chaos and the steady fortifying presence of the Master Emerald.

"So which way?" Sonic asked, interrupting this pleasant interlude. "Tell me you know a dry route."

Knuckles shrugged. ""This is Hydrocity. Very little of it is dry. How d'you feel about boats?"

Sonic made a face.

"On a scale of 1 to 10 where 10 is 'dry land' and 1 is 'underwater? About a 2."

Tails smiled and Knuckles took this as agreement and lead off, relishing the chance to at last be back on his own ground, running a familiar route. In spite of his remark to Sonic, and a lingering surprise that, of all the things for the hedgehog to baulk at, he simply couldn't swim, Knuckles did take them the driest route possible. An easy detour here and there to trigger sluices and pumps cost little enough time.

Some water though was, of course, unavoidable.

He glanced sideways at Sonic who was running steadily at his side.

"You like going fast, right?"

Sonic returned the look with an expression that indicated perfectly clearly that he considered the question a foolish one.

Knuckles cut sideways into a narrower tunnel, took three paces along it and then grabbed Sonic's hand and leapt into the air, as the tunnel gave out onto one of the flumes that criss-crossed the area. He twisted and landed on his back, pulling Sonic along with him so he could keep both their heads above water as they were swept along and round the watercourse.

Speed without effort.

Somewhere close behind Knuckles heard Tails splash into the water with them and a glance showed him right behind them, arms and legs wild, spinning on his backside in the current, completely out of control but laughing. The flume steepened abruptly and Sonic gave a yell which only had a slight hint of alarm left in it at the ride.

They shot out of the bottom of the flume so fast they skimmed the water below and fetched up amid the spray on a shallow slope of smooth stone.

Sonic staggered to his feet looking distinctly dazed and for a moment Knuckles wondered if he'd just started a fight by pulling such a stunt without warning, even though he suspected the look on Sonic's face pretty closely matched his own after that first tow.

Sonic shook his head ruefully and smiled.

"Well that was something! That what you do for kicks and giggles round here?"

Knuckles' knew his expression was perfectly composed "Just a shortcut, as long as you know where they end up."

Sonic scoffed. "Yeah right, pretend that wasn't for fun, all you like!"

"I don't know what you're implying." Knuckles said, firmly, but some combination of amusement adrenaline and sheer relief at being back on the Island made it hard to keep a smile from his face.

"Come on, I know somewhere safe we can rest tonight."

"Rest? Pah. Rest is for wimps," Sonic grinned and Knuckles ignored it. No one had slept since Chemical Plant, or eaten since the city, and they were finally somewhere that Knuckles could be certain was absolutely safe, and he wasn't going to miss the opportunity to get his head down even for a short while.

He pushed himself upright from where he'd been leaning against the wall and led the way up a twisting flight of stairs. Halfway up at a spot which look no different to any other spot he touched a place on the wall. With a smooth slide, a section of stone moved back and aside. Knuckles ducked his head to enter, beckoning the others after him.

"Secret passage!" Tails said.

"Never not cool," Sonic grinned at the fox's excitement.

Knuckles straightened once inside and closed the hidden doorway behind them. He looked around habitually checking the state of the place. It was an emergency refuge spot primarily, insurance against a day the waters were higher than expected and blocked the routes out, or there was some other urgent reason to be somewhere more secure for a while.

Luminescent algae glowed from a shallow, pool, but Knuckles found the candles anyway. He pulled the waxed fabric off a variety of boxes and opened the double-wrapped matches to light the candles and a small firebox in the centre of the room.

From another box he took food, dried fruit, grains, tea, jam, cooking tools. He filled a pan from the fresh water flow in the opposite corner to the pool and set it over the fire. They'd have to share on utensils. Then he sat back on the cork matting that covered one half of the space.

Tails was dabbling his fingers in the algae pool in curiosity but Sonic had stayed to watch Knuckles' preparations. He hadn't argued further about resting a while but looked puzzled instead.

"We're stopping down here?"

"It's closest," Knuckles explained. Sonic frowned. The hedgehog must really dislike the water.

"You don't want to get home now we're back here? This place isn't that big is it? Can't take too long?"

Now it was Knuckles' turn to frown, wondering why Sonic assumed this place was any less 'home' than anywhere else on the Island.

"I mean, shouldn't you tell someone you're back? You just vanished, someone must be worried." Sonic's expression changed briefly, and his voice lowered. "Sure, I know you said no family, right, but there's gotta be someone wondering where you're at. Even if it's only whoever gets sub-in shiny rock duty?"

Knuckles felt his jaw drop open and he stared at the hedgehog. He'd been sparing with details he knew, but this sparing? Sparing enough that Sonic didn't know? Eggman had known, hadn't he? How had Sonic not known?

"Knuckles?" Sonic's face had fallen into what was now recognisable as concern. "What'd I say?"

Knuckles shook his head trying to process why the realisation had rattled him. "Nothing. It's..."

Eggman had known. Had known his solitude here made him vulnerable. Susceptible. Easy to manipulate. To lie to.

Sonic hadn't known?

It wasn't dangerous for Sonic to know, Knuckles told himself, he'd thought Sonic already had known, there was no reason for the confirmation of it to feel like some new threat. Sonic, and Tails, were allies, hadn't he had ample proof of that already? All three of them would have been dead within the past few days multiple times over if not for both the other two.

Except that all that had happened without Sonic knowing.

Would it be different if he did? If he knew there was no support, no back-up, no fall-back plan, no obstacle other than one tired echidna and a handful of automated, ancient defences, defending this place and the power it held?

No. Surely no.

But every instinct railed against the admission and every self-doubt planted by Eggman's deception joined in the protesting chorus.

"Knux? Hey, it's okay, buddy." Sonic still looked puzzled but he smiled and shrugged. "You wanna rest here, we'll rest here. It's no big deal. Just a thought. Doesn't have to be the decision of the century. Tomorrow's not going anywhere."

Knuckles forced himself to meet Sonic's eyes, searching for any hint of deception and not remotely sure he'd recognise it if he found it.

Sonic tipped his head to the side.

"Okay?"

Knuckles shook his head minutely, by reflex more than in answer.

"There's no one waiting." He forced the words out. "There's no one else, there's no one here."

Tails looked up, eyes wide, and Sonic looked equally startled.

"How do you kn- What? Has something happened? Why… Did-"

Knuckles shook his head more firmly, cutting off the hedgehog's confusion. "Nothing's happened. Nothing new. No one else lives here. There are no other Guardians."

Tails stood up from his crouch by the pool.

"Knuckles…" He was frowning even more than Sonic and his ears were lowered. "But… No one? On the surface… Some of the books say that echidnas… that there are no more, that they're extinct. You… Are you saying, there's no one here either?"

Knuckles closed his eyes briefly. Part of him had already suspected as much – no one had ever come back after all – while another part occasionally wondered if there was some reason for that, that there was something that could be accounted for, that could change, that could make his solitary role explainable. That there was someone. Somewhere.

"There are no echidnas here. There's no one here. Only me."

"Knu-" Sonic started to speak but before he'd gotten more than one syllable out, Tails had launched himself from the pool and barrelled in at waist height, flinging his arms around Knuckles and knocking all the breath out of him. For a split section he thought he really was being attacked. He shot to his feet, Tails still clinging to him, and then froze, completely unable to find an appropriate reaction, unsure what to do with his own hands, which he'd flung up by reflex and now held in mid-air, as though halfway to either surrender or attack.

"That's horrible!" Tails' said, without letting go or looking up. "I'm so sorry."

Sonic's hand landed on Knuckles' shoulder making him snap his attention round to the hedgehog, but, while the expression on Sonic's face was strange, there was no threat there.

Knuckles looked down at the top of Tails' head and warily lowered his hands to pat him on the back.

"That's… Okay?" he said, looking to Sonic for further help but only getting a headshake.

"We didn't know," Sonic said and patted Tails' back more vigorously. "Come on buddy, you've already frightened the life out of Knux here, you can let go now."

Knuckles opened his mouth in reflex protest at the slight on his courage, but decided it was disrespectful to the little fox's fighting spirit.

"I've seen this one take on robots ten times his size," he said instead. "I'm perfectly entitled to be startled if he leaps at me."

Tails looked up.

"I didn't leap at you," he said, indignant despite what Knuckles had intended as a compliment.

"Kinda did..." Sonic said, but he was smiling. Tails released his grip and stood back. Sonic threw an arm around his shoulders and pulled him in for a moment before letting go as well. Tails leant in to the gesture without hesitation in spite of the teasing amusement in Sonic's tone.

Knuckles looked at the pair of them, feeling even more at a loss than he had a moment ago, and for lack of any better ideas returned to his position on the floor to attend to the fire and boiling water which by some miracle had not been overturned by the commotion.

After a moment Tails and Sonic joined him, watching as he poured half the water into the tea kettle then spooned dried grains and a handful of fruit into the remaining water before returning the pan to the fire.

"Are you hungry?" he asked, to break the silence that had descended.

"Yeah!" Tails said eagerly.

Sonic wrinkled his muzzle. "For porridge?" He waggled a hand "So so."

Knuckles wordlessly reached back into the supplies box and deposited a pot of honey in front of the hedgehog.

"Does that help?"

Sonic grinned. "You bet."

Eating was a somewhat awkward shared affair – Knuckles had equipped the place for one person, and they were going to empty what should have been a three day cache in one meal.

He couldn't quite bring himself to be concerned though. It was a relief to be on the Island. A relief to truly believe that Sonic and Tails were not going to about-face on him, even knowing the truth about his situation here.

Abruptly he found himself yawning.

Sonic tipped his head. "Do we need to set a watch?"

Knuckles shook his head and wondered at how easily the reaction came so soon after suspicion.

"No." He'd know if anyone else came here. And he was no longer afraid of what Sonic or Tails might do.

The proof of that came, even to himself, with how quickly and deeply he tumbled into sleep once they settled themselves down.

He drifted awake the following morning, with a clear sense of daylight, despite the underground location. Somewhere up above, the sun was warm and bright on the ground of the Island. He sat up and stretched. Sonic and Tails were both still asleep, the hedgehog flat on his belly with spines ruffled and askew from rolling over, and the fox curled in a ball with both tails wrapped around himself.

Knuckles stood and stretched and debated the safest way of waking them. Now he was rested he was keen to get back above ground, back to the Emerald, back to checking whether anything untoward had happened on the Island in his absence.

"Sonic!" he ended up calling loudly. "It's morning!"

The hedgehog gave a muffled, reluctant sound of acknowledgement and crawled to his knees, blinking sleepy disorientation from his eyes.

"'S still dark."

Knuckles relit a few more candles but shook his head. "Not outside."

Sonic opened his mouth, frowning but didn't actually get as far as a question before shrugging and turning to poke Tails in the ribs.

"Up and at 'em, kiddo!"

Tails' nose emerged from the bundle of fur that was the rest of him, and after a moment he sat up.

"It's morning?"

Knuckles nodded. Tails apparently accepted this at face value more easily than Sonic and only looked mournfully at the empty porridge pan.

Sonic got to his feet, following Tails' line of sight. "Uh, did we eat you out of house and home last night, Knux?"

Knuckles shrugged. "I can resupply. There's plenty stored and it's still growing season in most zones here anyway."

"Okay. Cool. So we going up top?"

Knuckles eyed the hedgehog as he bounced on his toes, no trace of sleepiness or recent awakening remaining. He glanced at Tails who shook himself and stood as well.

"I'm good to go," he smiled easily.

Knuckles led off without further comment, snuffing the candles as he went and leading the way through the twisting, canal-lined corridors to a tiny jetty where the stonework descended into the water once again. A sleek blue and gold boat rested low in the still water.

Sonic grimaced. "Oh. You meant it about boats?"

Knuckles gestured out across the water, where the water spread out from multiple channels into a wide underground canal basin.

"It's a choice of this then a long flight of stairs, or back the way we came underwater all the way then about 20 lockgates straight up. If you don't like the water this is the better route."

Sonic scowled at the boat a moment longer, then stepped to the edge to look down into the clear water before stepping back hurriedly.

Looking had been a mistake, Knuckles thought but didn't remark. This was the deepest open expanse in the city. Light spilled down from the sun tunnels directing daylight from the surface to be scattered by prismed windows and glitter from mirrored decoration. Rays of light shone through the crystal clear water to fade to deep blue than black as the depth increased. It was beautiful but if one didn't like water then the view was unlikely to have been reassuring.

Nevertheless Sonic reached for the high prow of the boat to steady himself and stepped aboard. The fox jumped on to join him, softening his landing with a flick of his tails so that the boat barely rocked. Knuckles unlooped the painters from the jetty and gathered them up in his hand. He stepped aboard, kicking gently away from the shore as he went.

Sonic dropped onto a bench and holding on to both sides of the boat, as Knuckles stepped half over and half around him heading for the stern as they drifted. He took up the long single paddle, and corrected their direction, but there was something off in the smooth motion of the craft.

He frowned and altered his stroke and started to make progress. Perhaps it was just the fidgeting of the hedgehog in the boat and the additional weight of two passengers when normally he was alone.

He was more than midway across and his arms starting to protest the additional drag before he was entirely convinced that something was really the matter with the boat. Surely it wasn't possible someone had been here in his absence?

He drew the paddle in and laid it down.

"What's the matter?" Sonic half turned, without letting go of the sides. "Don't stop!"

Knuckles shook his head, not sure himself yet and crouched down to reach over the edge of the boat and run his hand along the outside, below the waterline. It didn't take a second before his glove snagged on something instead of sliding over the smooth wood.

"What!" Sonic demanded as Tails moved to look and Knuckles held up a hand to stop him.

"The boat's been tampered with," Knuckles withdrew his hand.

This time Sonic's "What!" was twice the volume.

"Let me see," Tails said, but this time had the sense not to crowd over and unbalance the boat until Knuckles moved aside to allow him access.

The fox didn't stop at reaching and instead vaulted overboard, treading water and steadying himself with one hand on the boat while he stared at the device.

"Not good," was his verdict. "This is Eggman's."

Sonic's eyes widened.

"Row, Knuckles! We need to get off this boat, now! Tails get back in… or… no… get out. Fly. Is it a bomb?"

"A bomb?" Knuckles found himself repeating.

"Well I doubt it's a helpful little outboard motor is it?" Sonic snapped. "Tails?"

The fox shook his head. "It could be explosive. I don't know. I've nothing here to take it apart with."

Knuckles had started rowing again, Tails kicked his feet to stay with the boat as Sonic finally let go to pull him back on board.

How long did they have? How far away did they need to be? Should they abandon the boat?

No. None of them could swim fast enough to get clear. If they reached the other side then Sonic could perhaps run fast enough. Tails could perhaps fly high enough right here if he didn't carry either of them.

"Tails," Sonic started. He'd already realised the same thing Knuckles thought.

"I'm not leaving you two behind," Tails said firmly. "We don't even know if it's going to go off. Whether or not it knows it's been discovered."

The idea that a detonation might be triggered by their own interaction with it hadn't even occurred to Knuckles and he would have thrown even more effort into paddling if he hadn't already been using his full frantic effort.

Sonic and Tails crouched motionless in front of him, doing their best to make it no harder but the remaining seconds it took to the shore still seemed an age. Knuckles didn't slow down as they approached.

"Jump," he warned the others tightly. "I'm going to run us ashore."

Sonic and Tails were already leaping by the time the prow crunched against the brickwork and perhaps the impact was the trigger because the explosion was simultaneous. Knuckles was as much thrown as he was propelled by his jump into the air. He felt the flare of energy from rings and Emerald respond in unison but Sonic's hand was on his wrist before his feet had hit the floor and the instant acceleration was dizzying.

"Keep running," he yelled against the slipstream once he was able to wrap his head around the fact they were still alive. There was no telling what damage might have been done to stability of the dams and canals and mechanisms which directed the water.

"You think?" Sonic gasped, sarcasm audibly even though his panting breath.

Knuckles didn't bother with yelling more than the occasional direction after that. Some instinct was driving Sonic upwards in any case and that could only be a good thing.

Eventually he skidded to stop and they all stood a second, breath held, listening for any evidence of rushing water inbound. There was nothing, but Knuckles knew better than to take that as a sign of safety. Any number of controls could have been damaged, water could be creeping in any number of places it shouldn't, rising towards exits, drowning safe routes, rendering calm, navigable waters into torrents somewhere between where they stood and the outside air. He was deeply uneasy, a nagging, aching sense of imminent threat which had not faded with their distance from the explosion.

"We need to keep moving," he said.

Sonic nodded, then unexpectedly, grinned.

"Well since Eggman wrecked our last ride, seems only fair we borrow his." The hedgehog pointed and Knuckles belatedly assessed their location and saw what had drawn his notice. Tails was already running over to examine what was clearly one of Eggman's flying pods.

Knuckles had to fight not to look away. Eggman had been here. Had imposed himself deep in the Island's interior and – Knuckles' breath caught with the abrupt realisation – was still here.

That was the danger, not only the water, not only the explosion, the risk of falling stone, but intrusion. A clanging warning siren in his mind, tugging his attention in the opposite direction to safety, deeper into Hydrocity, to wherever the trespasser could be found.

"Knuckles?" Sonic broke across his thoughts. "Buddy, you're doing the whole 'tune out the hedgehog and get spacey' thing again. Can you not? What's wrong?"

Knuckles shook his head. It had to be his imagination. He was disturbed by finding the boat meddled with and by seeing the pod. He couldn't have missed Eggman's presence. Not for this long. Perhaps in the confusion of their arrival and near drowning, but never at rest, never in the quiet of their over-night.

"Eggman's here," he managed to reply when Sonic continued to wait expectantly for an explanation.

Tails turned away from the pod and made a face. He looked strangely unsurprised.

"I was afraid of that," he said. "I was scared the bomb on the boat might have a trigger based on us fiddling with it – but it could easily have had a comms alert instead. And we know the ruby can teleport people."

Knuckles stared at Tails. "You think he might have only just come back?"

Tails nodded and the mixture of relief on top of the sense of alarm made Knuckles close his eyes for a moment. He hadn't missed it. Not really. But how much time had passed for the boat to have been trapped, for the pod to be here? They'd time travelled but when had they come back to?

"I have to find him."

Sonic frowned. "You mispronounced 'we' there, Knux. We have to find him."

Knuckles hesitated, with his mouth already open to give directions to the surface while he headed back down to follow that sense of intrusion to its source.

Sonic raised his eyebrows and waited, too tapping out an urgent little rhythm on the wet stone that belied his stillness. Knuckles closed his mouth. Nodded tightly. Opened it again.

"I think I know where he is, but some of the route is almost certainly underwater by now."

"Well that sucks. Lead the way."

That seemed a totally contradictory response to Knuckles, but they didn't have time for him to figure it out, so he ignored it. Instead he eyed the pod. Taking it perhaps was not a bad idea after all. It gave them at least one extra option.

"Can one of you steer that thing?"

Sonic laughed. "I think Tails can't wait to try!"

In response Tails bounded aboard and beckoned. "Oh yeah, we have so got this!"

Sonic grinned and joined him. "We get pulled over by traffic, Knuckles has to be responsible adult."

Knuckles reached for a response but came up blank. Were they taking this seriously? And yet Sonic was ready to head straight back into the depth of the watery underground tunnels he cleared hated, so how could he possibly call him out for frivolity?

He closed his eyes as much to dismiss the puzzle as to concentrate on the direction they needed before instructing Tails.

It was a wobbly start with all three of them jammed into what was intended as a one-person craft, but the fox was a quick learner and was manoeuvring them adeptly enough by the time they reached the narrower routes.

"Left," Knuckles said as Tails slowed at a turning. The place Knuckles wanted to reach was to the south and below them yet, but this was the second shortest route he knew – the actual shortest they already ruled out on the basis of the amount of water seeping through the emergency flood doors when they'd reached them.

The thundering sense of danger and urgency was diminishing as they got closer, as though the Emerald or Island knew he was aware, knew he was coming. He could deal with Eggman, was eager to deal with him. Eager to put an end to this frantic runaround and confusion and fight after fight and being cast hither and thither until he hardly knew which way was up. At least here on the Island he knew his way, knew the dangers.

"Down there."

Tails sent them plummeting so fast Knuckles clutched instinctively for the edge of the pod but was distracted quickly enough by Sonic's yell.

"There! In the water!"

Tails threw the controls of the pod into reverse and brought them to a hover.

Sonic was right. Eggman was in the water and Knuckles frowned. The water wasn't safe here, was full of treacherous currents and undertows even without whatever damage had been done to the systems that controlled it.

Sonic looked at him, clearly in no hurry to jump in, and this time that was the right choice.

"Uh now what?"

"He's got a powered scuba suit." Tails leaned over to watch as Eggman powered away from them in spite of the currents. "What's he doing?"

"He's placing more explosives." Knuckles stared in horror, wracking his brains for any out. He would have one shot if he jumped in. If he grabbed Eggman first time then he could… what? He couldn't outswim the current down there. The best he could hope for was to take them both out together. Was Eggman enough of a threat to risk depriving the Emerald of its Guardian? He could use the Emerald maybe, but that was erratic, unreliable. There would be no guarantee. Was the risk big enough to justify it? How dangerous was this ruby?

The pod rocked as Tails leaned back towards the controls, muttering to himself and throwing switches.

Knuckles looked back at the water, half inclined to jump in anyway. He could almost see Eggman smirking at them as they hovered uselessly overhead.

Abruptly the pod vibrated violently.

"Tails..." Sonic started to ask but was interrupted by a sudden surge of water from below. It struck the bottom of the pod and spray cascaded up. Eggman floundered in the water below them.

"Don't you remember it Sonic? We've seen this particular pod before – from the wrong end though!"

Sonic grinned. "Oh yeah. Go for it!"

The pod moved lowering and closing on Eggman and then a second surge of water rose from below them, this time with Eggman splashing and flailing, and to judge from the look on his face, cursing, as he was borne upwards with it.

Sonic leaned out over the pod, recklessly far and made a grab for him. Knuckles hastened to help.

"Gotcha!" the hedgehog crowed as they both got a grip on an arm and dragged Eggman, half into the pod. He raised his head and grinned.

"Are you sure you wanted to?"

He twisted like a beached fish but reached a pack on his belt, pulled out another of the explosive charges and slapped it on the pod.

"Ten." he said calmly. "Nine."

"Bail out!" Sonic yelled. Tails grabbed him and rocketed upwards. Knuckles grabbed a blue ankle as it flashed past and was carried upwards and for a moment was certain they'd made it.

"Eight."

There was a yank on his own ankle and they were descending again. Knuckles looked down. A metal grappling claw tethered him and Eggman together and the weight was way too much for Tails at the top of the ridiculous stack.

"Seven."

The pod was still too close, and the water was lethal without the equipment which only Eggman had. Knuckles glanced up and saw the faces of Tails and Sonic looking down. Tails' face was screwed up in effort, clinging to Sonic. The hedgehog's was pure panic.

"Six."

"Tails, let go!" Sonic shouted.

Tails didn't.

Knuckles looked away. And let go.

The abrupt release of the additional weight sent Tails and Sonic hurtling upwards. He hoped Sonic would have the sense to tell Tails to keep going.

He hit the water kicking, in a flurry of limbs, striking out to try and free himself from Eggman's mechanical grip. The current already had them both and the surface and bottom of the channel swapped places in a tumbling, helpless spin. His head hit what had once been a step when this area was above water and his vision blurred. Where was Eggman? Where was the surface? Where was any airpocket?

Something hit him in the swirling water and he flinched away in alarm. All of the explosives Eggman had been carrying were spinning and bobbing in the water along with him.

Knuckles fought back panic. The one of the boat had been impact triggered. One good knock and he'd be blown to bits before getting a chance to drown. Something hit him hard in the chest and it was all he could do not to sacrifice his remaining air in a yell. He thrust it away as though that could possibly do enough to help and then reached for it instead as he realised what it was. The several air canisters to Eggman's suit were also loose down here. The one that had hit him had disappeared out of reach but he grabbed the next and fumbled with it to task several gasping breaths.

Swimming was impossible. Keeping himself oriented, clear of obstacles and getting the occasional gasp of air to breath was the bare minimum he could manage. The channel switchbacked around a corner and one of Eggman's devices loomed up ahead. Lit up and clearly already re-occupied and taking aim.

Knuckles took a chance and kicked one of the floating depth charges towards it. If it was drown, get blown up, or get shot, then he had nothing to lose.

This time he was lucky and the current snatched the kicked charge, turning it into a vicious projectile. The shockwave from the explosion as it struck Eggman's sub slammed through the water and for a few seconds Knuckles was deaf and blind and breathless, aware of nothing but Emerald energy racing through every limb like a feverish shudder. When he opened his eyes Eggman's sub had retreated again and he was suddenly aware of the cold of the water seeping into every limb. It was almost welcome. A contrast to the burning need for air which had his lungs on fire with the effort not to breathe.

His chest scraped the rough stone floor of the channel and he was dragged along it for long seconds until he clumsily pushed himself away with arms that felt way heavier than they should. He fell back onto his face and only then realised that he was laying in waist deep water, the current rushing over him but not longer carrying him with it.

Even so he nearly couldn't lift his face out of the flow, almost too exhausted to rise and how stupid would that be to drown at last in a bare few hands breadths of water? He rose to to his hands and knees, trembling and collapsed into a half sitting, half kneeling slump.

He nearly didn't notice the water starting to rise again. It was almost a surprise to find that he still have the energy to get back to his feet, once driven by alarm. He looked up and around, trying to relocate himself and plan an escape route.

He was at the bottom of one of the huge sumps scattered around the zone. The only way out was the sluice gate the water had drained by, back the way he'd come, or climbing. And only one of those was viable right now with the water rising. He looked up, reassessing the distance although he knew it all too well. Wet walls, hundreds of lengths high.

He gathered his composure and reached for the steady presence of the Master Emerald, somewhere nearby, dry and warm. He'd need its strength as well as his own to have any hope of an out.

"Knuckles!"

He froze. Staring upwards in the direction of the shout.

"Look out!"

A ship was plummeting towards him – Eggman's sub, transformed into an aerial vehicle and pursued by the pod which he'd assumed destroyed, Sonic perched on the edge, halfway out already and launching himself towards Eggman. Knuckles leapt clear, clinging to the wall as the force of Sonic's blow drove the craft hard towards the surface of the water. Spray flew in all directions and there was a grinding of metallic gears and a shriek of damaged machinery as the device rose again. The water level surged and Knuckles lost his grip and slipped back under. He kicked and twisted in the water, weary limbs refusing to cooperate, and weary mind refusing to process in which direction the surface lay.

Hands closed on his and then he definitely was moving up. He blinked water out of his eyes and Tails grinned down at him.

"Gotcha."

Knuckles nodded vaguely, too busy breathing to speak. Somewhere below he was distantly aware of the crashing and tearing of metal as Sonic jumped up and down on the Eggman craft and then Tails was lowering him into the other pod and Sonic was dropping down beside him and there was relief that was more than simply the realisation of survival.

"He teleported away again," Sonic said. "You okay?"

Knuckles laid his head back against the edge of the pod, completely limp.

"He's gone."

"Yeah. I said." Sonic smiled. "Are. You. Okay? Breathing. Air?"

Knuckles nodded. He was moderately sure of that. It was why he was still alive that he couldn't yet understand.

"How did you find me?"

Sonic grimaced. "We didn't. You got lucky. We followed Eggman. Turns out his pods have a homing system."

"This pod didn't blow up."

"Nope."

"It was a trick." Knuckles closed his eyes. "Again."

"I guess. Sorry."

"You shouldn't have let go!" Tails burst in.

Knuckles looked at Sonic who gave a tiny shake of his head which warned against arguing in spite of the fact he'd been yelling at Tails himself to let him fall and get away himself.

"Yeah, we'll debate that when we don't all look like wet rags, okay, Tails?"

Tails scowled but returned his attention to flying the pod.

"Which way is out?" he demanded.

Sonic caught Knuckles' eye. And winked.

"Up," Knuckles said. "Up, and then I'll tell you from there."

Tails threw a switch and they accelerated upwards, leaving the remains of Eggman's intrusion laying half submerged below them.

The was midday when they emerged. The sun stood high overhead, and so bright it was dazzling after their stint underground. It was hard to believe that it was still so early in the day. Knuckles felt as though they'd been fighting in the dark and the wet for a hundred years.

"You got a nice packed lunch stashed somewhere, Knux?" Sonic asked, clearly feeling the same. "I reckon we've kinda worked off last night's supper."

Knuckles nodded and they abandoned the pod to walk to the nearest cache – he didn't want any of Eggman's tech anywhere near those places he might use as a refuge. Tracking worked both ways, regardless of the fact it have pulled him out of trouble this time.

"The Tornado is still up here," Tails said suddenly halfway through their meal, as though he'd only just remembered.

That seemed a long time ago to Knuckles as well.

Sonic tapped his fingers against his empty plate.

"Hmm. So where next. Where do we think Eggman's basing this insane lark out of?"

Tails shrugged. "Dunno. But the gear for tracing the ruby was in the Tornado. If Eggman's hasn't been at it, that's our best bet."

Fed and watered, they ran back to where Tails had left the aircraft. While the fox examined the machine for tampering, Knuckles examined the area, looking for pretty much the same thing. He was restless. The idea that Eggman had been here, in his absence, long enough to interfere in Hydrocity weighed on him. What else could have happened? He needed to comb the whole Island, to reassure himself, to remove – again – all trace of the intruder.

"All clear!" Tails called happily and Knuckles looked round. The fox was still clambering over the aircraft. "Not much space though with all this tracking gear aboard. It'll be a squash even with you on the wing, Sonic."

Knuckles made nothing in particular of this remark until Sonic turned to stare from him back to Tails.

"Tails…" Sonic hesitated. "I don't… know that Knuckles is coming with us?"

Knuckles stared in turn at both of them. The question hadn't even crossed his mind. He was back on the Island. Neither Eggman, nor his new weapon were here any more. It ought to feel like the end of it, surely.

The end of his part in it.

So why didn't it?

Because Eggman was still a threat? Because with the ruby he could still come back? That was a loose end. But Sonic had that well in hand. Didn't he? Sonic certainly didn't need his help. Whether he owed it or not.

Knuckles frowned. He did owe it perhaps.

He started a mental tally but got no further than the most recent dousing. It was a hopeless endeavour. Sonic had pulled him out of trouble, he'd pulled Sonic of trouble. It was uncountable and in any case none of it outweighed the first time. Outweighed Sonic going on when he couldn't, retrieving the Master Emerald when he couldn't. Returning it when Knuckles couldn't have stopped him from refusing to do so.

There was nothing Sonic couldn't ask him for in recompense and he'd asked for nothing at all.

Just the thought of how it could have gone instead made Knuckles reach out on instinct to the Emerald he hadn't even laid eyes on since returning. Serene and untouched, at least as of yet, it calmed him. There was no answer to the problem there, but the still calmness of mind that the touch of it required was enough to let him see he own decision making more clearly.

He was going, and all his stewing about it was because he wasn't sure if he should. One way or another, this fight of Sonic's was his now too.

"I'm going," he said. Sonic grinned. Hugely and out of all proportion to Knuckles' expectations.

"Awesome!" the hedgehog said. "Good to have you. Let's go show Eggman what he's up against!"

Tails looked round a smile on his face as well.

"All aboard!"