I spend my time in isolation trying to decide whether or not to tell the others about the threat we face. It should be a straightforward call - they have a right to know. But I'm worried about how they'll react. They kill reviveds because they see them as monsters. If I told them that we need to eat brains to survive, and that we're being denied the gruel because of my refusal to play ball with Dr. Cerveris and Josh, they might rip me to pieces. Literally.

I've seen them do it to others. Killing gives them a buzz, and it's bull when they say that they only do it because they have to. There's a good chance they'll slaughter me if I tell them the truth, in the hope that Dr. Cerveris will restore their rations if I'm removed from the equation. A lot of normal people would sacrifice me in a situation like this, so I can't expect too much compassion from a pack of semiliving beasts.

Then again, maybe they deserve the benefit of the doubt. It's wrong to let them perish in ignorance. And if they kill me, what of it? I'll be brain-dead in a couple of days anyway. Why drag the rest of them down with me?

"Because they're bastards," I mutter, and brood about it some more.

Everyone's sour as stale yogurt the next day. The lack of nutrients is kicking in big-time. The zom heads are wincing at noises, groaning as hunger pangs shoot through them. They can't understand why they're being denied the gray gloop or why they feel as rough as they do.

"We must have done something wrong," Tiberius insists as they knock the issue back and forth.

"Nah," Gokhan says. "It's a test, innit? They want to see what we do when we get hungry."

"I'll rip Reilly's head off," Peder growls. "That'll show them what I do."

"It isn't Reilly's fault," Danny says. "He's not enjoying this. It's bloody Josh who's behind it."

"No it's not," Cathy shouts, then makes a face and lowers her voice. "It's Dr. Cerveris. Josh doesn't have any say in how they test us. It's the scientists who decide those things. I'll ask Josh what's going on the next time I see him."

"Oh, I'm sure he'll tell you," Tiberius simpers. "You mean so much to him."

Cathy flips him the finger, then glares at Rage. He's the calmest of everyone, watching an old episode of some American sitcom set in a bar, chuckling softly at the punch lines.

"I don't know why you're so happy," Cathy snarls. "You're part of this too. You'll starve with the rest of us, no matter how many arses you kiss."

"Chill, baby," Rage sniffs. "The Turk's right. They're testing us. Once they've compiled enough data, they'll feed us again. They need us. We're their blue-eyed darlings."

"Maybe they're feeding you on the sly," Danny challenges him. "Maybe that's why you don't seem bothered."

"Believe what you want," Rage shrugs.

"You never say a bad word against them, do you?" Peder spits. "You're a right muppet."

"I relish the easy life," Rage counters. "If we scratch their backs they'll scratch ours. You don't win any prizes for rubbing against the grain. I do what they tell me, treat them with respect and reap the rewards."

"Do you call being starved a reward?" Mark asks.

"Shut it, Worm," Rage snaps, then carries on talking to Peder as if he were the one who had asked the question. "They've got to treat me the same as everybody else when they're running a test, stands to reason. But in the normal run of things, by keeping them sweet, I get anything I ask for, films, games, magazines, even girls if I wanted."

Danny laughs out loud, ignoring the others as they moan and slam their hands over their ears. "Girls?" he shrieks. "What the hell would you want with those? We're all dead down below. We can't do anything with girls except look."

"That's why I said if I wanted," Rage replies smoothly.

Mark is frowning and staring at his groin. This is news to me. I hadn't realized the boys were impotent, though now that I consider it, it makes sense - no blood flow to stir their sleeping soldiers. If the situation weren't so dire, I'd have a good old chuckle about it. But they've more important things to worry about than dodgy machinery in their boxer shorts. And on impulse, having listened to them waffle on about this all day without saying a word, I suddenly decide to solve the mystery for them.

"It's because of me. They're starving you because I won't torture the reviveds. And they're not gonna stop until..."

I draw to a halt. Everyone is staring at me, even Rage, who doesn't look so cocky anymore.

"Go on," Tiberius says stiffly.

"The gray junk they've been feeding us is human brains."

"We know," Tiberius says.

"You know?" I exclaim.

He shrugs. "It's obvious. We figured that out months ago. Zombies eat brains, everyone knows that."

"You never told me," I huff.

"We didn't know that we needed to," Tiberius sneers. "How thick are you?"

"Enough of that," Rage snaps, getting to his feet. He looks uneasy. "Finish what you were going to say."

"We need the brains to stay conscious," I mutter. "Without regular feeds we'll lose our senses and become reviveds again. And if we do, we can't recover, we'll be stuck like that forever."

Rage stares at me coldly. Everybody else is gaping too.

"They told you this?" Cathy asks.

"Yeah."

"And you said nothing?" Her voice rises. "You let them starve us, knowing what would happen, not saying a word?"

"I'm telling you now."

"You bitch!" she shrieks. "That's the first thing you should have - "

"I'm calling Reilly," Rage says heavily. "I'm gonna tell him that you've agreed to do whatever they ask. Then we're gonna go tear some zombies to shreds and you'll hack them up, burn them, slice them into little pieces, and that will be that."

"No," I whisper. "They're people. I won't do it."

"You bloody well will," Rage snarls, stomping towards me.

I stand and face his challenge, hands by my sides. I don't flinch when he makes a fist and holds it threateningly in front of my face.

"A beating won't change my mind," I tell him. "I've been in plenty of fights, taken more than my fair share of thrashings. I took them at home too - my dad was handy with his fists, knocked me and Mum around all the time. You can smash me to a pulp, break my arms, snap my fingers, rip my ears off. It won't matter. I won't give in."

"I'll kill you," Rage croaks.

"Maybe," I concede. "I'll fight back, and I think Josh will stop you before it gets that far, but if you're tough enough and fast enough, maybe you can finish me off before they intervene."

"Do it," Danny says flatly, stepping up beside Rage. "I'll help."

"Me too," Gokhan growls.

"What about the rest of you?" Rage barks.

"I dunno," Peder says, looking worried. "She's not like the other zombies that we kill. She's one of us."

"But she won't be if they don't feed her," Cathy says, then frowns. "How long before we change?" she asks me.

"No one can last more than a week without being fed, so a few days at most."

Cathy's face hardens. "Kill her. If she's going to revert anyway, we should off her while we can. Otherwise we'll all turn into reviveds."

"No," Mark moans. "We can't do this. It's not right. It's murder."

"But if it's us or her..." Rage says heavily.

Tiberius pushes past Rage and glares at me. I wait for him to condemn me too, but to my surprise he comes out with something bizarre. "I was named after Captain Kirk in Star Trek."

Everyone stares.

"I tell people I was named after the river in Rome, but really it was after Kirk. His full name was James Tiberius Kirk. My mum and dad loved Star Trek. They made me watch it all the time when I was growing up. Except they didn't have to make me - I loved it as much as they did. Kirk was my hero."

"Is this going somewhere, or have you lost your marbles?" Danny huffs.

"Kirk always stood up for the underdog," Tiberius says. "Every week, him and his crew risked their lives to save others. They killed the bad guys when they had to, but they never killed innocents, not even to save themselves."

"That was just a TV show," Cathy jeers.

Tiberius nods. "I know. But it was right. I watched Kirk, Bones and the rest of them, and I knew they were doing the right thing. I was sure I'd do the same thing in their position. I used to hope that one day something dangerous would happen to me, so that I could prove how brave and loyal and human I was.

"Reviveds are different," Tiberius says, facing Rage. "I don't think Kirk would have fought for a load of mindless, walking corpses. But Peder's right - B's one of us. If we kill her, we really will be monsters. And I'm not prepared to let that happen. I'll fight with her if I have to, die with her if it comes to that."

Rage holds Tiberius's gaze, deliberating. The others await his verdict. Finally he grunts and looks aside.

"We'll think it through some more," he mutters. "I'll have a chat with Reilly, see if there's another way to sort this out. But if there isn't... well, we'll discuss that tomorrow. See how we all feel about it then."

Rage returns to his couch and the others disperse, shooting me dark looks. Mark and Tiberius remain. Mark's trembling. Tiberius is stiff as a mannequin.

"Thanks," I mutter, knowing the word isn't enough.

"Screw you," Tiberius says. "You're crazy, making a stand like this. Go away and have a rethink, then start cutting up zombies like you're told. Because if you don't, I doubt I can save you next time." He glances at me and I've never seen such an expression before, torn between pride and self-loathing. "I don't even know if I'll try."

Then he storms off and Mark slips away too, leaving me alone, hated, a pariah. But, against all the odds, they didn't kill me. I'm still alive.

But not, I suspect, for long.