The voice of the Kah-Gash whispers to me as we're climbing the stairs, stunning me by abruptly breaking its months-long silence. You can join with the others.

I pause, startled by its sudden and unexpected reappearance. Then, not wanting to let Beranabus know-he might toss Dervish aside in his eagerness to make enquiries of the Kah-Gash-I carry on as normal, addressing it internally. "What do you mean?"

Can't you feel the magic inside Bec and Kernel calling to you?

I have been feeling a strange tickling sensation since I stepped through the window. I put it down to chemical irritants in the air-one thing you can't say about the demon universe is that it's polluted. I've become accustomed to fume-free atmospheres. But now that the Kah-Gash has clued me in, I realise the tickling is the force within myself straining to unite with Bec and Kernel.

"What would happen if we joined?" I ask.

Wonders.

"Care to be a bit more specific?"

No, it answers smugly. I'm not sure if the Kah-Gash is a parasite feeding off me, or if it's woven into my flesh, a part of me like my heart or brain. But its voice bears echoes of mine. I've used that smart-alec tone more times than I can remember.

I'm worried about letting my piece of the Kah-Gash link with the other parts again. What would it do if I gave it free rein? Could we trust it?

You are the control mechanism, the voice says, the first time it's ever told me anything about the nature of itself. With my help, you can unify the pieces and unleash jour full power.

"But could we control it," I press, "and make the weapon do our bidding?"

To an extent, the voice answers cagily.

"What does that mean?" I grumble, but there's no reply. "Hello? Are you still there?"

Unite us, it says impatiently. Unleash me. Become the Kah-Gash.

"Without knowing what I'm letting myself in for? No bloody way!" I snort.

Coward, the Kah-Gash sneers, then falls silent. I feel the tickling sensation fade. I continue up the stairs, brooding on what the voice said and wondering what would have happened if I'd given in to it.

On the roof. Another Disciple, Sharmila Mukherji, was seriously wounded by Juni. Her legs are missing from the thighs down. Beranabus is working on the stumps, using magic to stop the bleeding and patch her up. She's unconscious. It doesn't look to me like she'll ever recover.

Dervish is resting on a hospital trolley. Meera's sitting beside him. Shark's guarding the door to the roof, to turn back any curious humans. The rest of us are gathered around Bec, listening to her story.

She tells us about Juni Swan, who's somehow come back to life in a cancerous mockery of a body. Bec says Juni is insane, but more powerful than before. Dervish blasted her from the roof, catching her by surprise when he recovered from the coma he'd been in since his heart attack. I want to go after her, to finish her off, but Bec is adept at sensing where people and demons are, and she says Juni has already fled. Revenge will have to wait for another night.

I thought it would be awkward being around Bec, that she'd remind me of Bill-E, that I'd feel resentful. When he died, she took over his corpse, came back to life, then remoulded the flesh in her original image. In effect, she stole his body. But there's nothing of my half-brother apart from the occasional word or gesture. I have no trouble thinking of her as a separate person with the same right to exist as any other.

Bec speaks quickly, detailing how werewolves attacked our home in Carcery Vale, backed up by humans with guns. She tells us she can absorb people's memories when she touches them. When grappling with a werewolf, she learnt it was a Grady boy who'd been handed to the Lambs to be executed. But the Lambs-executioners set up to dispose of teens with the lycanthropic family curse-didn't kill him. Instead they kept him alive, and found a way to use him and other werewolves as trained killers.

"You're sure the Lambs masterminded the attack in Carcery Vale?" I ask.

"I can't be certain," Bec says. "We didn't see any humans. Sharmila wanted to go after the Lambs once Dervish was safe, but we decided to wait until we'd discussed it with you. The werewolves might have been the work of some other group..."

"But they were definitely teenagers who'd been given to the Lambs?" I press. If she's right about this, we have a known enemy to target. If she's wrong, I don't want to waste time chasing an irritating but harmless gang of humans.

"Yes," Bec says. "At least the one I touched was. I don't know about the others."

"They must have been," I mutter. "I've never heard of anyone outside our family being inflicted with the wolfen curse. But why?" I glance at Dervish. "Have you been rubbing Prae Athim up the wrong way?" She's the head honcho of the Lambs. Her and Dervish don't see eye to eye on a number of issues.

"I haven't seen her since she paid us that visit before Slawter," Dervish answers, looking bewildered. "I've got to say, I don't have much time for Prae, but this isn't her style. I could understand it if they were after something-you, for instance, to dissect you and try to find a cure for lycanthropy-but there was nothing in this for them. Those who set the werewolves loose wanted us dead. The Lambs don't go in for mindless, wholesale slaughter."

"But if not the Lambs, who?" Kernel asks.

"I think Lord Loss was behind the attacks," Bec says. "Maybe he realised I was part of the Kah-Gash and wanted to eliminate the threat I pose, or perhaps he just wanted to kill Dervish and me for revenge. The attack tonight by Juni Swan makes me surer than ever that he sent the werewolves. It can't be coincidence."

"Juni Swan," Beranabus echoes, with the guilty look that crosses his face whenever talk turns to his ex-assistant. "I'd never have thought poor Nadia could turn into such a hideous creature. I don't know how she survived." He looks at Bec. "Your spirit flourished after death, but you're part of the Kah-Gash. Juni isn't. Lord Loss must have separated her soul from her body some way, just before her death. That's why he took her corpse when he fled. But I don't understand how he did it."

He mulls it over, then curses. "It doesn't matter. We can worry about her later. You're right-Lord Loss sent the werewolves. I cast spells on Carcery Vale to prevent crossings, except for in the secret cellar, where any demon who did cross would be confined. Even if he found a way around those spells, he would have been afraid to risk a direct confrontation. If he opened a window, the air would have been saturated with magic. You and Dervish could have tapped into that. You were powerful in the cave, stronger than Lord Loss in some ways. He probably thought humans and werewolves stood a better chance of killing you. But that doesn't explain why the Lambs agreed to help him. Or, if they weren't Lambs, how they got their hands on the werewolves."

"Maybe he struck a deal with them," Dervish says. "Promised them the cure for lycanthropy if they helped him murder Bec and me."

"Would they agree to such a deal?" Beranabus asks.

"Possibly."

"Prae Athim's daughter turned into a werewolf," I say softly, recalling my previous meeting with the icy-eyed Lambs leader. "She's still alive. A person will go to all manner of crazy lengths when family's involved." I shoot Dervish a wink.

"An intriguing mystery," Beranabus snorts. "But we can't waste any more time on it. We have more important matters to deal with, not least the good health of Dervish and Miss Mukherji-they'll both be dead soon if we don't take them to the demon universe. Open a window, Kernel."

Kernel eagerly sets to work on a window. His eyes have held up so far, but they won't last indefinitely. The problem with building body parts in the demon universe is they don't work on this world. If he stays too long, Kernel will end up blind as a bat again, with a pair of gooey sockets instead of eyes.

"I'm not going," Dervish says.

"You can't stay here," Beranabus replies quickly, angrily.

"I have to. They attacked me... my home... my friends. I can't let that pass. I have to pursue them. Find out why. Extract revenge."

"Later," Beranabus sniffs.

"No," Dervish growls. "Now." He gets off the trolley and almost collapses. Meera grabs him and holds him up. He smiles at her, then glares at Beranabus. He might be within a whisker of death, but that hasn't affected my uncle's fighting spirit.

"It would help if we knew," Meera says quietly in defence of Dervish. "The attack on Dervish and Bec might have been a trial run. The werewolves could be set loose on other Disciples."

"That's not my problem," Beranabus says callously He's never been overly bothered about his supporters, and always stresses the fact that they sought him out and chose to follow him-he didn't recruit them.

"There's been a huge increase in crossings," Meera says, which is troubling news to me. "We've seen five or six times the usual activity in recent months. The Disciples are stretched thinly, struggling to cope. If several were picked off by werewolves and assassins, thousands of innocents would die."

"It might be related," Kernel says, pausing and looking back.

"Related to what?" Bec asks, but Beranabus waves her question away. He's frowning, waiting for Kernel to continue.

"This could be part of the Shadow's plan," Kernel elaborates. "It could be trying to create scores of windows so that its army of demons can break through at once. We'll need the Disciples if that's the case-we can't be everywhere at the same time to stop them all."

"Maybe," Beranabus hums. "But that doesn't alter the fact that Dervish will last about five minutes if we leave him here."

"I'll be fine," Dervish snarls.

"No," Beranabus says. "Your heart is finished. You'll die within days. That's not a guess," he adds when Dervish starts to argue. "And you wouldn't be able to do much during that time, apart from wheeze and clutch your chest a lot."

Dervish stares at the magician, badly shaken. I'm appalled too. "It's really that bad?" Dervish croaks.

Beranabus nods, and I can see that he's enjoying bringing Dervish down a peg. He doesn't like people who challenge his authority. "In the universe of magic, you might survive. Here, you're a dead man walking."

"Then get him there quick," I say instantly. "I'll stay."

"Not you too," Beranabus groans. "What did I do to deserve as stubborn and reckless a pair as you?"

"It makes sense," I insist calmly. "If the attacks were Lord Loss trying to get even, they're irrelevant. But if they're related to the Shadow, we need to know. I can confront the Lambs, find out if they're mixed up with the demon master, stop them if they are."

"Is the Shadow the creature we saw in the cave?" Bec asks.

"Aye," Beranabus says. "We haven't learnt much about it, except that it's put together an army of demons and is working hard to launch them across to our world." He stares at me, frowning. He doesn't want to admit that I might have a valid point, but I can tell by his scowl that he knows I do.

"You'd operate alone?" he asks sceptically.

"I'd need help." I glance around. Shark's an obvious choice. I can channel a lot of magic here, but there are times when it pays to have a thickly built thug on your side. But I'll need someone sharp too-I don't have the biggest of brainboxes. "Shark and Meera," I say, with what I hope sounds like authority. Shark can't hear me, but to my surprise Meera responds negatively.

"I want to stay with Dervish," she says.

"He'll be fine," I tell her, trying to sound confident, not wanting them to know how nervous I feel-I've never taken on a mission like this before. "He has Beranabus and Bec to look after him. Unless you want to leave Bec with me?" I ask the magician.

"No," he mumbles, as I guessed he would. "If you're staying, I'll take her to replace you."

"Then go," I say. "Chase the truth on your side. I'll do the same here. If I discover no link between Lord Loss and the Lambs, I'll return. If they are working for him, I'll cull the whole bloody lot."

Kernel grunts and a green window opens. "Time to decide," he tells Beranabus. I look from the magician to Meera. She's not happy, but she doesn't raise any further objections.

"Very well," Beranabus snaps. "But listen to Shark and Meera, heed their advice and contact me before you go running up against the likes of Lord Loss or the Shadow." He picks up the unconscious Sharmila. "Follow me, Bec," he says curtly and steps through the window.

Bec stares at us, confused. I flash her a quick grin of support, which she misses. Meera steps up to her and asks if she's OK. Before I can hear her reply, Dervish is hugging me, squeezing me tight.

"I don't want to leave you," he says, and I can tell he's struggling not to cry. I have a lump in my throat too.

"You have to go," I tell him. "You'll die if you stay here."

"Maybe that would be the easiest thing," he sighs.

I squeeze his ribs until he gasps. "Don't you dare give up," I snarl. "Mum and Dad... Gret and Bill-E... they'd give anything to be where you are now-alive. It doesn't matter how much pain you're in or how sorry you feel for yourself. Alive is better than dead. Always."

"When did you become the sensible one?" Dervish scowls.

"When you became a pathetic mess," I tell him lightly.

"Oh," he grins. "Thanks for clearing that up." He clasps the back of my neck and glares into my eyes. "Be careful, Grubbs. If you die before me, I'll be mad as hell."

"Don't worry," I laugh. "I'll outlive you by decades. I'll be dancing on your grave fifty years from now, just wait and see."

Dervish smiles shakily, then releases me and staggers through the window, massaging his chest with one hand, just about managing not to weep. I hate watching him go. I wish he could stay or that I could leave with him. But wishes don't mean a damn when you've been selected by the universe to spend your life fighting demons.

"Sorry we couldn't have more of a chat," I say to Bec, and I genuinely mean it. I'd like to sit down with her and listen to her full story, learn what life was like sixteen hundred years ago, what she makes of the world now, if Riverdance is anything like the real deal.

"Next time," she smiles.

"Yeah," I grunt, not believing for a second that our paths will cross again. In this game you soon learn not to take anything good for granted. The chances are that Bec or I-probably both-will perish at the hands of demons long before the universes can throw us back together.

I think about bidding Kernel farewell, but he doesn't look interested in saying goodbye, so I simply wave at him. He half-waves back, already focusing on Bec. She's his companion now. I mean nothing to him if I'm not by his side, so he won't waste time worrying about me. I know how he feels because I feel the same way about him.

"Come on," I say to a slightly befuddled-looking Meera. "Let's go and break the news to Shark. Do you think he'll mind us volunteering him for a life or death mission?"

"No," Meera sighs as we cross the roof to the doorway. "That dumb goon would be offended if we left him out."