As if she was in some horrible dream, Rose found herself taking slow-mo steps through the inky water. There was a pressure in her head, and beneath that a sort of prickling, tickling, stinging feeling.

Like little insects with blowtorches were welding odd bits of her brain together.

She tried to ignore it, to concentrate on breathing. Her chest no longer rose and fell; it felt numb, dead flesh. She was aware only of a burning itch on both cheeks as she walked one step after the other, sliding through the thick Thames mud, tripping over slimy obstacles.

She saw everything around her in a sick green light, half-lurching, half-swimming onwards with the others until they reached the narrow mouth of a pipe in the dark wall.

Two creatures that might once have been men guarded it. They looked like pale, translucent corpses. Their eyes were like big grey jellyfish eating into their faces.

"Go through," One croaked, standing aside. Rose heard him clear as day – how could that be when she was under water? She pondered the riddle as she squeezed after the others into the pipeline, dragged herself along through the water. Someone crawled in front of her, someone behind. She didn't know who they were. But it didn't matter.

They were all a part of the hive now.

Not for the first time, Mickey was wondering how come he ever let the Doctor talk him into doing anything.

He'd meant it about going down the tubes. Or more accurately, down Aldgate tube. It was now 6 a.m. and the underground station was just opening.

Mickey eyed the ticket barrier.

"Gonna use your sonic screwdriver?"

The Doctor seemed affronted.

"Do I look like your average fare dodger?"

"Barriers don't normally apply to you" Peter chuckled.

"Cheeky." The Doctor turned to Mickey "Get yourself a single. And get us one each too, while you're at it." Mickey tutted but then eyed Peter suspiciously.

"I know his excuse," He nodded at the Doctor. "But what's yours? Royalty don't carry cash?"

"Firstly I'm an imperial. Secondly I don't live here any more. Kinda makes it hard for cash flow" He reminded him.

Once through the barriers, the Doctor ran down to the empty platform and sonicked open a STAFF ONLY door in the side of the wall. It gave on to a little cupboard space full of hard hats, torches, emergency equipment. Leading off from there was a narrow access corridor, ending in another locked door, marked for authorised service personnel only. Soon the hum of the screwdriver was filling the little room.

"Either of you any good with phones?" He asked.

"Only at running up bills," Mickey said whilst Peter merely shrugged.

With the lock shocked to bits, the Doctor opened the door to reveal a cramped, circular tunnel, sloping downwards at an alarming angle. The walls were a thick spaghetti of coloured wiring all the way round. Thick plastic bands grouped the wires into bunches and provided footholds.

"Phone lines. Secret government link-up, in case of nuclear war," The Doctor whispered. "This is hidden London, boys."

"It can stay hidden, it's horrible" Mickey replied, turning up his nose.

"Look at those webs. No one's been down here for years." Peter added.

"Till now. Because what Crayshaw and his mates don't seem to realise is that this conduit passes within just a few inches of the decontamination chamber. And from there we can get inside and face these creatures in their lair." He grinned. "I know where that is, by the way."

"We passed it while on the run from the marines," Peter realised.

"That's the thing about hindsight, it's always twenty-twenty."

"So you can get us inside – maybe. What then?" Mickey asked.

"I need to talk with these creatures" The Doctor replied.

"They didn't seem keen on talking when they called by before, did they?" Peter protested. "What d'you think they're gonna do – put the kettle on and give you a biscuit?"

"Wouldn't that be marvellously civilised!" The Doctor's grin faded. "If I'm going to stop them, I need to know what it is I'm going to stop. Cheer up – now their evil plans are in full swing and nothing stands in their way, maybe they'll be feeling chattier."

"Yeah. Cheerful thought." Mickey frowned, pointed to the tunnel. "Hang on, you said this goes past a few inches from that chamber thing, right? A few inches of what?"

"Solid concrete."

"You are so joking me!"

"It's all right!" The Doctor brandished the sonic screwdriver. "I'm getting quite good at resonating concrete."

"You can crack open concrete with that?" Peter questioned. The Doctor grinned and merely shrugged.

"Well, I'm getting freaked at the thought of going down there." Mickey said, glancing down the forbidding tunnel.

"Come on Mickey. It's not that bad." Peter said, looking forward to the challenge facing them.

"Plus it's probably the best place we could be," The Doctor told them. "Not many people about to filch water from. Less chance of Rose's image coming back to haunt us." He started to climb inside, then glanced back and fixed Mickey and Peter with his large, piercing eyes. "I don't want to see her like that again. Do you?"

Mickey and Peter glanced at each other for a moment.

"Then let's find her before we get a chance to." Peter said. They then climbed in after him, and they began their cautious descent into the narrow passage.

Strung out with nerves, aching with tiredness, Vida wondered what time it was. Andrew, Rose, all those poor people had been pushed into the river, unprotesting, off like livestock to the slaughter. Soon, Crayshaw assured her, there would be more victims 'acclimatising' in the darkness.

To her uneasy relief she had been moved on to dry land. The morning sun was rising steadily, yet there was no one about on this side of the bank. Across the bridge it was a circus of police cars, troop carriers and ambulances as a yelling, jostling swarm of people pressed in on the roadblocks and barriers. It was pointless even to think of shouting for help, and clearly Crayshaw knew it. He had seized her arm in a punishing grip and marched her into the reception of Stanchion House.

Hope flickered as the glass doors slid open. If she could only signal to somebody that she was in trouble. . .

Not a chance. The place was entirely deserted. No receptionist. No Derek guarding the lifts. Nobody.

"Where is everyone?" She demanded. "What have you done with them?"

"Arrange the meeting with Kelper," Said Crayshaw.

"Why can't you do it yourself?"

"I am deemed to be obstructive. It will be easier if he suspects nothing. Call him on your personal phone."

She pulled her mobile from her pocket. If only the water had damaged it, if only. . .

"I'm out of power," She said, disbelievingly. "The battery's dead. His private cell number's programmed in and I can't access it!" She thrust the phone in Crayshaw's old face, triumphantly. Whatever happened, at least she knew she couldn't be held accountable. She hadn't helped these things, and whatever they did now-

"Vida? What the hell is going on around here? I just strolled in. What the hell has happened to security?"

She jumped as if she'd been poked with a stick. A massive man in full naval dress uniform was striding towards them, brass, brocade and decorations shining in the strong reception lights. It was him, Kelper, accompanied by a young aide. "All London's gone crazy." The vice admiral's nasal tones filled the reception like the drone of an engine. "I had to fly in to Bletchley and take a chopper out here. Couldn't reach Andrew, or you –"

Vida opened her mouth to speak, but Crayshaw got there first:

"We can reach Andrew."

Her mouth dried. She offered a hopeless look of vague apology, then watched Crayshaw with frightened eyes as the two men exchanged formal greetings. "Miss Swann informs me you have arrived to inspect the wreck of the Ascendant yourself, Vice Admiral," Said Crayshaw.

Kelper spoke frankly.

"Your administration of this affair seems to be a mess, John. I've found government ministers chasing their tails, a lack of communication between the naval ranks, a general absence of explanation as to how the Ascendant came to be in bits at the bottom of the sea. . . A conspiracy of silence which extends to the fate and whereabouts of certain chemical tracers Miss Swann's department had placed upon that ship."

"There is no conspiracy, I assure you," Said Crayshaw, all smiles, crossing to the lift. "You must inspect our underground laboratories for yourself."

The doors slid smoothly open.

"Must we go now?" Said Vida awkwardly. "Perhaps we should adjourn to one of the briefing rooms and –"

"The sooner this matter is ended, the better," He said casually. "And Andrew Dolan is already down there. We should really see how he is faring."

Kelper and his aide looked inquiringly at Vida. She looked at the floor, her frantic thoughts piling up, crowding her head. This thing held Andrew, Rose, so many others in its power, and if she messed up now they would never be saved. But then, was there even the tiniest chance that this hive thing wearing Crayshaw's body would keep its word, whatever she did?

"Run!" She shouted suddenly, grabbing hold of Kelper's braided sleeve, and yanking him away from Crayshaw. He hesitated, confused. She tugged on his arm again, dragged him away. "He needs something from you, I don't know what!"

The aide seemed about to protest when Crayshaw grabbed him by the back of the neck and flung him with superhuman force inside the lift. He smashed head-first against the wall and slumped down. "How many more times!" Vida yelled. "Run!"

She started to drag Kelper after her. But as she heard water splash under her soles, she knew it was already too late.

A carnival procession of pale, bloated freaks stood blocking the turnstiles out of the reception. Her blood chilled at the sight of the Victorian lady, the pirate and the U-boat captain who had come for her before, their eyes silvery, fat and ruined. But there were many others now: a dark-haired child in Regency lace, a group of young sailors in bell-bottoms, an old man in a stained apron. They stood ranged in silence, water trickling steadily from their noses and mouths.

"As I said, sir. . ." Crayshaw had removed his dark glasses, and now they could see the scabrous pearls that bulged obscenely from under his lids. "The sooner this matter is ended, the better."

Rose felt the bodies crushing in around her. How many were there now in the black reaches of this flooded pit? She shut out the thought.

It was easier, better to think of the faces in her head. A blonde woman, care and concern behind the glare in her eyes, her scent so familiar and warm Rose could cry. Mum? Mum, where are you? A man, burly and staring with close-cropped hair – no, that image blurred into another, youthful and friendly with quirky good looks. His eyes gleamed with secrets he would share only with her, and. . . Doctor, I want you here. . . a black boy with a scally smile and warm arms. . . Mickey, say you never did that. . . girl-friends reeking of clubs and smoke and hastily sucked mints. . . I trusted you. . . Then Peter appeared. Tall, toned and tanned, his cheeky and toothy wolfish smile only added to his charm... he was like the brother she'd never had. His calm silvery eyes locked in everything and held it secure... He'd tried to save her...

They would come to her. Yes, that was a lovely thought. They cared and they would come to get her out of here before the feast began.

Keisha was drifting in and out of an uneasy sleep, totally drained. Her life felt so messed up and mixed around she had become numb to it.

Now and then, something would jolt her awake – the sound of Jackie bustling around the flat in an attempt to keep herself busy, or the grave voice of the man on the TV news.

". . . putting guards on the sewers to stop them getting into the Thames that way. The number of people drawn to the river from all over the country continues to grow, and the terrifying possibility remains that soon the army will be unable to hold them back. . ."

Keisha hit the mute button, a low, panicky feeling in her stomach.

Her mum should have called by now. Had she not got to her flat yet? What if she'd not called in, and had gone straight to the river instead? The thought gnawed at her.

Soon she pulled out her mobile and dialled the mobile number she'd dialled back at the flat. The number her mum had called on.

Just the answer phone. She hung up. Her mum sounded happy, perky on the message. She'd never sounded that way when she'd been home.

"It's all going to pot," Said Jackie softly, joining Keisha on the sofa. "Everyone's going out of their minds."

Keisha put away the phone.

"They're being tricked."

"And there's not even any spaceships in the sky."

"We've gotta stay right here," Keisha told her, and Jackie nodded. "Whatever happens, we know it ain't real." She paused. "I hope my mum gets here soon."

"I wish my mum was here," Jackie agreed, feeling for Keisha's hand.

She found it – then squeezed hard, hard enough to break fingers.

"Ow! Jackie, what're you –"

Then Keisha saw the ghost of Rose, sad-eyed and dripping, in front of the TV. The image stared at them, saying nothing. "Mickey never did nothing," Said Keisha, trembling. "I made it up. I was stupid, I. . . "

But the ghost of Rose just opened up her arms, ready to give them both a big, wet hug.

"Please," She whispered.

"I'm coming, sweetheart," Said Jackie, and Keisha was already getting up off the sofa, crossing to the door.

Rose looked so grateful as she splashed away to nothing.

"We've been crawling through these tunnels for ever," Mickey complained, his voice sounding unnaturally loud in the confined space. "When are we gonna get somewhere?"

"We are somewhere," The Doctor retorted, ducking down a new path in this cramped maze of concrete and spaghetti wiring. "Junction X2, there you go, says so on the wall."

"Junction X2? What's that supposed to mean?" Peter asked.

"Means we're probably close to the decon chamber."

"Means we're lost!" Mickey called.

"We are not lost. I don't do lost."

Mickey nodded to Peter.

"We're lost." He nodded back.

"I know."

"Not listening." The Doctor told them.

"Lost!" Mickey countered.

"Blah, blah, blah, can't hear you."

On they went through the concrete catacombs.

Vida was shoved into the lift after Kelper, propelled by cold, dead hands.

"What the hell is happening?" He stared in horror at the ice-white, bloated faces pressing in around them, crowding into the enclosed space, trampling the aide underfoot. "What are these things?"

"Creatures from space," Vida gasped as the lift door slid closed. "The source of those alien proteins in the sea samples."

"We are close to the spawning time," Said Crayshaw over the smooth whine of the lift descending. "And so you are needed, Vice Admiral Kelper. The ships of your navy must help to spread us. We must create new power bases. Harbours. Inlets. Great lakes. All will be as one with us."

Kelper sneered and shook his head.

"You're crazy."

Crayshaw replaced his dark glasses.

"You will soon come to see things as we do."

Vida looked over at Kelper, feeling sick with fear.

"He's going to drown us." Then the pirate's fingers wormed over her lips, rubbery and wet like tentacles, silencing her as the lift softly jarred to a stop.

The Victorian woman did the same to Kelper as the doors whooshed open.

There was a clatter, a sudden hubbub, and at once Vida saw why the building above ground had seemed so deserted. Everyone was down here in the secret labs. Soldiers, security guards, cleaners, they milled about in this vast, antiseptic landscape of gleaming tiles and plastic partitions, dwarfed by the ship cross-sections that littered the space like unlikely sculptures.

The squad leader came forward to address Crayshaw while his fellows held back, staring uneasily as the sinister crowd spilled from the lift.

"Sir, we've been waiting for your orders. Surely the protection of this building and the wreck outside should be our priority, not these labs?"

"We've all been stuck down here for hours," Snapped the cleaning woman, clearly too tired and angry to be afraid, "While you're mucking about having a fancy-dress party. I've got to get on, you know!"

Everyone jumped except Crayshaw as the doors to the decontamination room ground open. Heads craned to watch the dark hole open up like a wound in the sterile chamber. Vida tensed herself but nothing and nobody came out. She struggled in the icy grip of the pirate ghoul, tried to speak through his thick, wrinkled fingers, but it was no good.

"Sir?" The squad leader turned back to Crayshaw, edgy and uncertain. "Your orders, sir?"

Suddenly, with a rushing, thundering roar, a wave of filthy water came flooding in through the decon doors. It smashed against the remnants of the Ascendant with incredible force, as if eager to pound them to nothing. And as it sped towards the horrified crowd it seemed to rear up like some impossible animal. Guns exploded in a deafening rattle as the soldiers fired wildly, uselessly into the grey, churning mass.

"Your orders are to drown for us, soldier" Called Crayshaw. "We no longer require your protection. But don't fear. As the spark of life leaves your bodies, newness will awaken inside you."

Vida and the vice admiral were thrust forward to join the others.

The body of the aide was thrown after them, knocking Vida to the gleaming floor. And as the water crashed down towards her, she saw Crayshaw had cracked a happy grin.