The natural tunnels merged into neater, carved ones with doorways and rooms leading off them. Ianto got the feeling that he was walking through a lost city that had been submerged. It was dry underfoot still, and after a period of shouting that echoed down the corridors and seemed to come from every angle it was utterly quiet. He came to a guard room where two Okrani lay dead, and passed on into a large chamber. The dead lay all around the room as if there had been a fight, and Ianto shuddered to think of what could have done it. Quiet voices emerged from a darker doorway, and he crept through the carnage towards them.

Steps led down from the door, carved into the rock, and wound around the edge of the chamber. As he expected, he found another chamber at the bottom, smaller than the one above and lit by a single swaying lamp that burned bright, spluttering white. Jack lay gagged and bound on a bench, squirming away from the lone Okrani that stood over him with a knife.

"I'm going to bleed you," the Okrani snarled. "Hear you scream."

Ianto drew his gun and shot before the Okrani could move again and hurried forwards to drag it off Jack, who sobbed and lunged towards him. He caught Jack up and stroked his bare skin reassuringly whilst he fumbled at the knots binding his arms behind his back. "I've got you, you're safe. It's okay, I've got you."

As soon as his hands were free, Jack reached up to rip the gag out and returned to clinging to Ianto. "I'm sorry. I'm so, so sorry."

"It's alright, it's alright." He kissed Jack's temple and started rocking him. "I've got you now."

They pulled themselves together, holding onto each other tightly. Jack's clothes had been taken, and he searched around the room desperately. "Ianto, they took it, they took it. It's over..."

"No, they didn't get it." He caught Jack's hands and held him still. "I took it before they could get to you."

"Give it to me." Jack scrabbled at him until Ianto returned the device to him and he could clutch it to his chest. "I'm sorry; it's got its claws in me so badly."

"It's alright, I had figured that out." He kissed Jack once more and passed him a jumper. "We'll get rid of it soon and then everything will be fine."

Jack slumped against him and nodded. "I want to go home. I want this to be over."

"We will be soon." Ianto held him tighter, helped him into clothes from his own pack and then guided him out and onwards, through the lost city.

# # #

"We need to keep them distracted," the Doctor muttered, pacing the length of the control centre and running his hands through his hair. "We need to make sure that Jack and Ianto are free to do what they need to, if they've got through the tunnel."

"Can you stop with the 'if'," Martin snapped. "Nothing can happen to Jack, and he won't let anything happen to Ianto. They'll get there."

"If... if we help them." The Doctor stopped and leaned on a table. "But how can we divert them?"

"We can draw their forces away from their base," Rick stated. "Marsam and Marsa Alam are too close, they can respond too quickly. We need to draw their forces north."

"No, no, we're not going to fight."

"Yes we are." They all turned and looked at Rick. "Doctor, fighting is all we have. We've proved our strength - they'll take the challenge. Nothing else will draw them out."

The Doctor started pacing again, shaking his head. "You can travel north, keep moving, draw them out and try - try - not to engage them. There's been too much loss of life already."

"Sometimes our lives are all we have to give," Tosh commented. "If that's what we've got, it'll have to do."

# # #

They drove north along the coast after dawn the next day, passing abandoned settlements and signs of battle everywhere they passed. By sunset they had reached the ruined remains of the city of Suez, and they set up camp there in the skeletal buildings whilst the tail of the convoy rolled into the city.

They got an uneasy night's sleep, broken by animalistic cries in the darkness. Dawn, though, came in stillness and silence, without even the cry of a bird to break the eerie quiet.

Overnight, the harbour had filled with elegant, fragile-looking boats. Their delicate appearance was in stark contrast to the bristling darkness of the Okrani swarming on their decks. Tosh watched the boats approach, wrapping her arms tighter around her chest, and spoke without turning to look at the footsteps approaching behind her. "I've faced the end of the world before," she told them, "but never with such certainty."

"The Doctor's going to parlay." Rick squeezed her shoulder, and when she looked at him at last he gave her a wry smile. "That should keep them busy, at least. Buy us some time."

"But we have no idea how much time we need," she pointed out. "Jack and Ianto could be days away from their goal, they could be captured or... Sorry. Think positive, right?"

"That's the spirit." They fell silent to watch the boats approaching, carried on a dry, hot breeze.

The front boat broke away from the flotilla, picking up speed towards the shore. A lone figure stood at the prow, and as they came closer Tosh recognised the figure as a tall woman, human at least in appearance, with wildly curling golden hair, dressed in fine silver-blue robes that billowed around her and with heavy silver jewellery set with large blue stones at her throat, wrists and waist. In her hand was a long, elegantly twisted staff.

When the boat ground up onto the shore, the woman used her staff to swing herself down onto the beach, and only paused to collect a bag from the boat before she began to pick her way up over the rocks.

They stretched out in a line on either side of the Doctor to meet her. She seemed unworried by their stony faces and the number of weapons they carried, even though she carried only a gun and the staff, and her hands were too full to reach them.

"I brought you a gift," she told them with evident glee when she got close enough, tossing the sack ahead of her at the Doctor's feet before covering the last few feet with greater ease. "It's something from your friend. I thought you might want a token of him."

The Doctor kept glaring at her, so Rick stepped forwards and collected the bag. Whilst the woman grinned at them, he reached in and pulled out the edge of a piece of dirty, ripped white material. He pulled more out and found a piece of blue material. It was only when he had them both out that Tosh recognised them as clothes - Jack's clothes. She gasped and felt Owen stiffen beside her.

"Oh you do know him," the woman crowed. "I thought we were going to have to play that silly game where you pretend not to care about him."

"Where is he?" Owen demanded. "What have you done to him?"

"He was caught trying to break into your masters' base," she told him, shaking her head disapprovingly. "I think he learned his lesson before the end, though. It took such a long time to teach him." She leaned on her staff and smiled up at the sky. "You can keep those. He doesn't need them anymore, after all."

"River," the Doctor snapped. "What are you doing here?"

The woman grinned at him. "Hello Sweetie."

They all turned, as one, to look at the Doctor, who strode up to her and crowded into her personal space. She carried on grinning at him, and didn't even flinch when he leaned closer to peer at her. "Did you use the psychedelic lip-gloss on them?"

She looked disgusted at the idea. "Have you smelled their breath? There are some levels that even I won't sink to. No, our Lashimi overlords needed someone non-threatening with a good grasp of languages and an understanding of the planet's culture and political structure to liaise with the local communities and make the take-over go more smoothly."

He chuckled. "And what happened to that person?"

"Oh, him I used the psychedelic lip-gloss on." She tapped her lips. "I'm safe now, though."

The Doctor shook his head. "What are you doing here?"

"They sent me - well, him - to talk to you. You can't win against them, Doctor." He went to turn away and she grabbed his arm, looking sincere for the first time in the conversation. "Take the people you care about and go, please. You can't fight..."

"Go where?" He shook his head and dragged his arm out of her grip. "And you have one of the people I care about. I can't leave him."

Rick growled. "Doctor, who is this?"

"This," the Doctor gestured at her. "Is River Song. Intergalactic pest, but a good woman despite it," he added grudgingly.

She smirked at their confused glares. "I try my best."

# # #

The lost city looked to have been abandoned recently. The sand was scuffed up and scattered with broken and forgotten equipment. They picked their way through the passages, with Jack leaning heavily on Ianto. He stumbled often, weakened by the attack in the tunnel and his capture. Ianto had to drag him along at times and stop for him, waiting until he could get up again and go on.

Eventually the carved tunnels dropped suddenly and grew damp and water stained, then they met steel and glass tunnels, sealed against the pressure of the water. They crept in and through the passages, put off-kilter by the eerie silence and the emptiness. Here too there were signs of abandonment, as if the forces had left quickly, but there was a greater feel of watchfulness.

Ianto thought that he was asleep and dreaming when they turned a corner and found themselves in a control room, but he was in too much pain for it to be a dream. He drew his gun again and took up position by the door, looking over at Jack and smiling encouragingly. "This is it, then. Can you do it from here?"

Jack staggered to the control panel and sank into the chair, trembling hands reaching for the desk. "I don't... I don't know."

He frowned at him and stepped towards him. "What, is it not the right place?"

"No, it's the... the song. I can't go against it. I'm sorry." He gripped the desk, white knuckled, and Ianto realised that he was fighting against a stronger impulse. "I can't... Ianto."

A sharp pain on the back of his head reminded him that he'd turned his back on the tunnel and he slumped against the wall, vision fogging for a moment. The sounds of a struggle were distant as if heard through water, and the world swayed when he dragged himself to his feet. Andrea and Jack were fighting; she was clinging to his back and clawing at him whilst he tried to dislodge her. Blood ran from a deep scrape on his cheek where she'd nearly caught his eye.

The device lay abandoned on the floor, kicked out of the way in the struggle, its lights blinking softly. Ianto shook his head to clear the dizziness and the edge of its influence and staggered across the floor to it. As soon as he touched it he felt it pushing at his mind, trying to get control. Wires and cables cluttered the desk, and Ianto found one that looked right, jammed it into one of the ports on the side of the device and plugged the other end into the computers.

Immediately the screens lit up, flashing red and black, and both Jack and Serki fell to their knees with their hands over their ears. Even Ianto could feel the mental control the machines exerted failing and spluttering nonsense at him, but it hadn't had time to get into his mind - not like it had for Jack. He fell to his knees beside Jack and wrapped his arms around him, holding him tight. "I've got you. Please be alright."

The machinery was spitting out sparks and smoke, and alarms were ringing throughout the structure. Ianto gathered Jack up and started hauling him out of the control room, back the way they'd come. He started sobbing when Jack fell still in his arms and slumped to the ground to hold him. "I'm sorry," he whispered into Jack's hair. "I can't go on. I'll be here for you."

He combed his fingers through Jack's filthy hair and tried not to hear the creaking of the failing seals and the roar of building fires in the control room.

# # #

The boats with the army had got closer, and River stepped back towards them. "Doctor, I can't stop them unless you surrender."

"We won't," Rick insisted before the Doctor could. "We have to fight."

She looked back at her army once more and tossed her staff aside, striding towards them to take her place in their line and reaching for her gun. "Then I guess I'll have to join you." She looked sideways at the Doctor. "Can't let you die."

He smiled absently. "Can't let you die, either. Spoilers."

The first boats touched the shore and the confused created by River's defection dissipated as the first soldiers leapt into the water to stream up the beach. They fell back towards the UNIT troops and everyone reached for their weapons. The Okrani hoard swarmed towards them and around them, surrounding them and trapping them on the flat tarmac before the beach. Tosh reached out and felt Owen take her hand for a moment. "This could be it," she whispered.

"It was going to come eventually." He released her hand and steadied his gun in both hands. "I never thought I'd die in battle."

"It's strange, isn't it?" The army kept coming, more and more of them swarming across the ships that had already disgorged their hoard. The more they came, the more futile the fight seemed. She sighed and set her shoulders. "This is for Jack and Ianto."

Rick was next to her and glanced down at her, nodding his agreement. "For Jack and Ianto."

At last, the Okrani had all disembarked the boats, and their army surrounded the UNIT force more than a dozen deep on all sides. They roared and shrieked, bashing their weapons together to create a din that drowned out Owen's next words. Tosh could barely think over the sound of it.

And then it stopped.

Silence descended on the waterfront and hung in the air, as fragile as glass, then, like glass, it shattered. Their strange chittering turned frantic and confused, they turned this way and that, lost and dismayed, and turned away from the battle. Whilst the UNIT troops watched in bewilderment, the Okrani fled, some towards the sea, some towards the desert, and some into the city. The Doctor straightened his bow tie and turned to them. "I believe that was a message from Jack and Ianto." He raised his voice and rocked back on his heels. "The Lashimi's system has been destroyed. Their controls are neutralised. Earth is safe!"

The cheer that rippled through the crowd was drowned out by an almighty explosion far out in the sea, which sent water fountaining up. Tosh only had to look at the Doctor to know that Jack and Ianto had been in there.

# # #

Jack gasped back to life, reaching out for Ianto and the song at the same time. Ianto was there, his arms loose around Jack, and the song was silent. He forced himself to sit up, stirring Ianto, and shook him. "Ianto. God, Ianto."

"'m here," he mumbled, raising his head with difficulty. "Jack."

"Come on." His head was throbbing but apparently not as much as Ianto's, so he grabbed him and hauled him to his feet. "We have to go."

Ianto was a dead weight against him, a reversal of roles, and carrying him was sapping Jack's renewed, adrenaline-fuelled strength. He stumbled repeatedly, tripping over his feet and Jack, and no matter how hard he tried he seemed unable to support his own weight. They'd barely got any distance before he had to lean his whole weight on Jack just to keep upright, and soon after he pitched forwards, dragging out of Jack's arms and falling to the floor with a weak cry.

He dropped to his knees beside him and rolled him over, cradling him in his lap. "Ianto? Ianto, stay with me," he begged.

"Here," Ianto breathed, curling towards Jack. "I'm sorry."

"Don't." He curled over him awkwardly and kissed him. "You'll be fine. Just save your strength."

Ianto smiled up at him. "You knew what I was apologising for."

He shook his head fiercely. "No. Not now we've come so far."

"I don't have much choice." He rubbed his head against Jack's stomach and groaned when Jack pulled him into a sitting position. His head dropped to Jack's shoulder instead. "Remember me, please?"

"Forever," he promised, choking on tears. "Please don't leave me."

Ianto smiled and closed his eyes. "I wish I were in Cardiff. But as long as I'm with you."

"Ianto..." He choked and held him closer. "I love you."

He got no response.

The base was creaking around them, passages filling with smoke from fires whilst streams of water started pouring in through the seals as the pressure decreased. A door ahead of them burst open, forced in by the pressure of the water bearing down on them, and the rush caught them up and dragged them along. The force pressed them together, and the last thought Jack had before he succumbed to the pressure was that he was glad he hadn't let go.