Soldiers are battling with zombies at the end of the corridor. A small group of humans, no more than four or five, against a dozen or more of the living dead. The soldiers have guns and are firing openly on their enemies, but unless the bullets strike their heads and rip the zombies' brains apart, they don't do any real damage. And the zombies aren't giving the soldiers the time or space to squeeze in many clear headshots.

My first instinct is to try to help the soldiers. It doesn't matter that they've been keeping me captive, or that they've been deliberately starving me for the last few days. I feel compelled to help the living.

The zombies have the soldiers surrounded. I start towards them, shouting, trying to distract the undead killers. I'm not sure how I plan to help the humans, but at least I can fight off the zombies without fear of being infected. Maybe I can buy the soldiers time to retreat to safety.

But the reviveds put an early end to my half-formed plans. They press in close, dig in teeth and fingers, and it's all over before I hit the scene. They leave the humans before they fully turn, somehow knowing they've done enough.

The soldiers writhe on the ground and scream for help or mercy, but there's nothing anyone can do for them now. One puts a gun to his head and ends the nightmare before it can claim him. The others suffer on.

The zombies bunch together in front of me and sniff the air, pressing forward dangerously. I remember what happened during the experiment. The reviveds don't react to zom heads unless we attack them. It's hard, but I force myself to stand calmly as they circle me, fingers flexing, nostrils dilated.

They decide I'm one of them, lose interest in me and press on, moving with purpose. Soon I'm left with the soldiers, who are all vomiting and transforming. I can hear bones forcing their way out through fingers and toes, teeth thickening and lengthening. Turning my back on the doomed, screaming men, I make for zom HQ, hoping to find answers or safety there.

It's the first time I've been able to patrol the corridors by myself. Under normal circumstances I wouldn't get very far, but virtually all of the doors are open. The security system has either crashed or been hacked. There's nothing to hold me back. But that means there's nothing to hold back the zombies either. Or that grisly clown. Mr. Dowling could be lurking in any of the rooms that I pass or around any of the corners that I come to.

But there's no sign of the clown. I scope lots of zombies, and a few soldiers and scientists running for their lives, but that's all.

I'm close to zom HQ when a Klaxon starts to wail. The high-pitched sound is torturous and I collapse to my knees, choking with pain. Clasping my hands over my ears doesn't help. I feel like my head is about to split. I see zombies falling like ninepins, moaning and convulsing. It looks like the revolt has been quashed. Some bright spark has come to the rescue. It's probably for the best. As much as I hate the crew here for what they've done to me, I don't want to see them all slaughtered. I'll just wait, ride out the pain as best I can, and put up no resistance when they come to take me back to my...

The Klaxon dies away as swiftly as it blared into life. The zombies rise and shake their heads. They snarl accusingly at the ceiling, then press on in search of fresh victims, back in business, as hungry as ever.

I stagger on until I find zom HQ, but the door here is closed and doesn't open when I push. I pound on it and roar out names. "Rage! Reilly! Tiberius!" But nothing happens.

I'm not sure what to do now. I back away from the door, staring at it sullenly. An undead woman with one arm staggers past. She stops and turns, eyes widening with delight, lips splitting into an eager smile. Then a bullet rips through her forehead and tears her brain to shreds. She collapses with a soft wheezing noise.

I glance over my shoulder and spot Reilly and Dr. Cerveris jogging towards me. Gokhan, Peder and Cathy are with them. Reilly looks scared but in control. Dr. Cerveris just looks furious.

"How did you get out of your cell?" the doctor snaps as they draw level.

"The clown opened my door."

Everyone gapes at me.

"What bloody clown?" Reilly grunts.

"Mr. Dowling." I look around. "Nobody else saw him?"

"She's started to hallucinate," Dr. Cerveris huffs. "That's common among revitalizeds in the final stages of consciousness. We should leave her. She could regress at any time."

"They're all in bad shape," Reilly says, pointing to the others, who are shaking and dizzy-looking. "If we're going to try to save the rest, we might as well save B too."

"Very well," Dr. Cerveris mutters. "But if I give the command, blow her brains out and don't stop to think about it."

The doctor steps forward, presses his fingers to the panel on the zom HQ door, then puts an eye up to the retinal scanner. The door slides open and he looks inside. "Nobody home," he says, closing the door again.

"Why don't we hole up in there?" Peder asks. "The zombies couldn't get in if we shut the door behind us."

"Of course they could," Dr. Cerveris barks. "Members of staff have been turned. We know from past tests that certain operational memories remain among reviveds. Some of the soldiers and medics might recall what they need to do to open locked doors, and if they had clearance when they were alive, they still have it now."

"So what are we going to do?" I growl. "Run around like slasher-movie fodder until the zombies get us?"

"First we fetch the others," Reilly says as we pad down the corridor, following the animated Dr. Cerveris. "Then we lock ourselves into a room that requires a digital code. The reviveds won't be able to recall a string of numbers - their memories aren't that strong."

"How come you're bothering with us?" Cathy asks as we run. "Did Josh tell you to help us?"

"I haven't seen him," Reilly says. "I don't know if he's still alive. But it's our job to protect you. We're under attack. An outside crew has disabled our system and freed the reviveds, and their forces are still active. I thought we were safe when the Klaxon kicked in, but obviously they got to that too. I don't think they're interested in the reviveds - they can find more of them anywhere - so they must be after you guys."

"I've put too much work into this project to see it hijacked now," Dr. Cerveris says petulantly. "Once we've run off these invaders, I'll track down whoever was responsible for the attack and flay their flesh from their hides."

"So you aren't helping us out of humanitarian concern?" I jeer.

"Of course not," Dr. Cerveris says. "You aren't human."

I shake my head admiringly. He might be a son of a bitch, but at least he stays true to himself, even during a crisis.

We pick up Tiberius from his cell - it's quiet down his corridor and he had no idea that anything was amiss - then push on. A couple of corners later, we run into a pair of reviveds. They go wild when they catch the scent of Reilly and Dr. Cerveris. They hurl themselves at the humans. Reilly fires but misses. Before the zombies can take him, we wrestle them to the ground and hold them there while Reilly takes aim and shoots.

I hate doing this, helping him kill, but we have no choice. It's Reilly and Dr. Cerveris or the reviveds. And while my sympathies should lie with the zombies who've been imprisoned and maltreated, I can't stop thinking of myself as one of the living.

Mark's cell is next on our route. The door's open but he's cowering inside, hunched over in a corner, tears streaming down his face. (Those new drops are miraculous. Even with everything else that's going on, I feel a stab of jealousy and wonder why the rest of us have been denied them.)

"Mark!" Reilly barks. "Get your arse in gear. We're moving out."

Mark looks up and shakes his head. He opens his mouth to say something, but nothing emerges.

"What's wrong?" I ask, stepping towards him.

"Leave the little worm," Cathy grunts.

"Yeah," Gokhan sneers. "He's acting like a baby, eh?"

"He's coming with us," Dr. Cerveris says with unusual warmth. He shoves past me and crouches by Mark's side. "Come on, Mark. We have to get out of here. We're going to take you to a safe place."

Mark stares at the scientist. A shadow flickers across his eyes and for a moment it looks to me as if he blinked. But of course that's impossible. The drops are good, but nothing can be that good, not for a zom head with paralyzed eyelids.

"Is he out there?" Mark whimpers, his gaze shooting towards the open doorway.

"Who?" Dr. Cerveris frowns.

Mark's gloved right hand is twitching by his side, fingers drumming the floor. But when I steal a closer look, I realize he isn't drumming - he's squashing. There are lots of dark smudges on either side of him. They could be ink blots, but I know that they're not.

They're smeared spiders.

"You saw the clown," I say, and Mark's eyes lock on mine.

"You saw him too?" he gasps.

I nod heavily. "Mr. Dowling."

"The button," Mark croaks.

It wasn't a hallucination. I'd started to doubt myself, but now I know for sure that my giggling visitor was real. There's no time to wonder at it, though. We have to get out of here and find sanctuary.

"Come on." I take Mark's hand and haul him to his feet. "We need to get away before the clown comes back."

That puts a rocket under Mark's arse and he bounces away from me and is first out the door.