We march slowly but steadily, saying little, following the marbles. I try to keep track of time and distance, but it's impossible. Sometimes, I wish a demon would attack, just to break the monotony, but we see none of Lord Loss' familiars. We can't even sleep - our bodies get weary, but we can't shut off our brains.

Eventually, we come to a point where two enormous black panels meet at a ninety degree angle and run up to the roof of yellowish sky. The panels are several feet wide and half a foot thick. They stand alone in the rocky surroundings, eerily out of place.

"Have you seen the film 2001: A Space Odyssey?" Dervish asks after a minute of silence.

"No. Why?"

"This reminds me of it." He walks round the black pillars, squinting at them, then says in a curiously flat voice, "Good morning, Dave."

"Who's Dave?"

Dervish laughs. "Doesn't matter." He looks at me, eyebrow cocked. "What do you think they are?"

"A place where four squares of the Board meet."

"Me too. But why just these weird slivers of black? I would have expected walls stretching the entire length of the boundaries."

"Why don't we step through one and see? I mean, we'll have to anyway, since the marbles were heading that way." The marbles stopped when we did, and now hang a few inches short of the black panel on our left.

"Let's try the right panel first," Dervish suggests. "Just for the hell of it."

"OK." I pick the marbles out of the air and put them in my pocket.

Dervish tests the panel, sticking a hand through to make sure we can pass. "It's OK," he says. "We - "

Suddenly, with a startled grunt, he disappears, hauled through the panel by something on the other side. I scream his name. When there's no response, I dart into the darkness after him.

It's not pitch-black like the maze, but very dark. I get glimpses of a demon wrapping itself round Dervish. Tentacles covered in long, glistening blades, slicing away at Dervish, cutting him open, blood flying in every direction.

I jam my hand into my trouser pocket. Yank out both marbles. Scream a word of magic at them, the word coming from somewhere deep inside me. Light flares, sharp and fierce in its orange brightness. I yell another word of magic as the light bursts forth, directing all the rays towards the demon.

The demon shrieks with pain from the explosion of light. It has dozens of eyes, a necessity in this dark kingdom, but a handicap when strong light's trained on it. With another agonised cry, it releases Dervish and hurls itself away, sheltering its eyes with its tentacles.

I grab Dervish and throw him back through the panel, which is white on this side. Then I reverse out after him, at the last possible second commanding the marbles to follow, stepping through at the same time as they slip out of the dark zone, so I don't lose track of them.

Dervish is on the volcanic floor, healing his wounds with magic, angry for being caught out so easily. "Thanks," he mutters.

"Don't worry about it." I squat next to him. "Can I help?"

"No. I'll be fine once I patch myself up."

"A few of your spikes were cut off," I tell him, tapping his head.

"Maybe I'd be better off bald like you," he laughs, then makes the hair grow back to its proper length.

When he's healed himself, he stands, checks for any cuts he might have missed, then warily faces the other black panel. "There could be a similar monster through there. Or worse."

I say nothing. I want to volunteer to go ahead of him, to test the waters, but I'm afraid. Sheepishly hoping Dervish will take the lead.

Dervish breathes out through his nose, then glances at me. "Ready to save my bacon again?"

"If I have to," I chuckle then give the order for the marbles to lead us to Shark. They float through the panel into blackness. We follow.

Space. Freezing emptiness. Not even air. A moment of complete dizziness and suffocating panic. Then instinct makes me surround myself with a force field of warmth and air. Dervish has done the same and is floating beside me, staring around with happy wonder. His mouth moves, but I can't hear what he's saying. I point to my ears and shake my head. He tries again, then makes a tube of air grow from his force field to mine. When it touches, he speaks and this time I hear him. "I always wanted to be a spaceman, like Flash Gordon. It was my dream."

"Me too," I smile. "Except I wanted to be a real astronaut, like Neil Armstrong or Buzz Aldrin. Walk on the moon."

"It's bizarre, isn't it?"

"Yeah. Like when we were on top of the cloud, but stranger."

Dervish does a slow somersault. It looks graceful at first, but he can't stop and keeps tumbling over and over. He yells for help, but I'm laughing too much at the freewheeling punk. Finally, he finds his balance, rights himself and glares at me. "Thanks for the help!"

"Do it again," I coo. "Whirl for me, Dervish, whirl!"

"I'll whirl my foot up your ass," he grumbles, then looks for the marbles. "Let's go find Shark."

"OK. But if you want to try your hand at gymnastics again, I'll be more than happy to - "

"Keep it up," he growls. "Keep it up!"

Laughing, I give the marbles their freedom and we drift forward again, leaving behind a pair of small white panels, glowing softly in the vacuum of sterile space.

I was wrong about this space being sterile. Though there don't seem to be any planets, the marbles eventually lead us towards a demon of unbelievable size. It's one of the vast sky demons. From the ground they looked huge, but up here it goes beyond words like massive and immense. This one must be hundreds of miles long, fifty or sixty high, a comet-sized, slug-like demon, drifting through the void of space in search of... what? Demons to kill and devour? Foes to fight? A world to settle on?

Dervish and I pause when the marbles home in on the demon. We look at each other bleakly. "If that thing spots us..." Dervish whispers.

"We're too small," I whisper back, even though there's no need - sound can't carry in space, so we should be able to speak as loudly as we like. "It won't bother with a couple of ants like us."

"Unless it enjoys squashing ants."

We want to pull back, detour around it or wait for it to pass. But the marbles keep tugging after the demon, urging us to follow. Since we've no other option, we glide after them as they lead us ever closer to the terrifying behemoth.

We come up underneath the monster's bulging stomach, which looks more like rock than flesh. The marbles pause next to the stomach wall. I get the sense they want to penetrate the demon's crusty shell. But then they take a turn and lead us forward, towards the creature's head.

Half an hour later, we float up from beneath the demon's gigantic lower jaw. I'm worried that, this close, the monster can't help but see us. But there's no evidence of any eyes. Either they're set much higher up its face or it's blind.

But there's definitely a mouth, running like a ridged valley from one side of the head to the other. Lips parted, teeth the size of large houses set in the rocky gums at irregular intervals. A tongue crawling with scores of smaller, parasitical demons, feeding on the remains of whatever this monster eats.

And amidst those demons, fighting for his life - Shark.

The warrior is in poor shape. These demons are weak compared with some of the others we've fought, small in size and power. But there are hundreds of them and they keep coming at him, fresh scavengers replacing the dead almost as soon as they've fallen. They're like tiny piranha bringing down a mighty ox.

"Shark!" Dervish bellows, but of course he can't hear. Dervish looks sideways at me, tilting his head instead of asking the question outright.

"I'm ready if you are," I tell him, though my stomach's tight with nerves.

"If the giant closes its mouth, I don't know if we could get out. Maybe only one of us should - "

"Don't tempt me," I stop him. "You and Shark risked everything to help me. It's only fair I do the same in return. So don't give me the option of cutting out on you now. I'm afraid I might take it."

Dervish grins. "Then let's go for a dip in the mouth of Moby Dick!"

Cavernous. No smells or sounds. Just the spectacle of legions of vicious demons wriggling over and around one another to take turns attacking the lonely but resilient Shark. They spot us when we enter. Dozens peel away from the main assault and hurl themselves at us. Small, furry, dark demons, like tumbleweed with claws and fangs. We swat them aside without slowing. We've come too far and seen too much to be scared by these hangers-on.

Shark glances up as we close in on him. His eyes are distant and I see that he thinks we're another couple of demons. He aims a fist at me, but I stop out of range. Dervish dips lower, trying to direct a tube of air at Shark so they can communicate. But Shark must think it's a tendril or tongue. He ducks, throws demons at Dervish, edges away from him, further back from the mouth. I flash on an image of what would happen if the monster swallows now. Quickly try to purge my mind of it.

I slip behind Shark and send out a tube of my own, all the time battling the demons. Shark spots the tube, dodges it, then leaps, hands outstretched, intent on throttling me.

Dervish flies forward and collides with Shark. They crash into me and our limbs get entangled. Now that we're touching, sharing our force fields, we can hear Shark. He's screaming madly, vile curses, words that make no sense, desperation and isolation thick in his throat.

"Shark!" Dervish roars. "It's us! Dervish and Kernel! We've come to rescue you. Stop fighting. We can get you out of here."

Shark screams in response, raises a large tattooed fist to pound Dervish flat, then pauses, faint lines of realisation rippling across his face.

"It's really us, Shark," I tell him. "This isn't a trick. We came for you."

"Impossible," he croaks. "How could you get here? You're illusions. Lord Loss sent you to torment me with hope."

"Don't be a dope," Dervish snaps. "Could any illusion look this good?"

Shark blinks - then grins. "How?" he whispers. "How did you find me?"

"We used magic."

"But it's empty space out there."

"So?"

"You mean... all this time... I could have left? I wasn't trapped? I didn't have to spend months... years... whatever... fighting these horrible furballs?"

"Nope," Dervish says lightly.

Shark's expression darkens. He grabs one of the demons and rips it to pieces, then uses its fur to wipe blood from his face. When he tosses the rag away, his features are composed. He sniffs as if what's happened is no big deal. "So much for the tour," he says casually. "Let's go find a bar."

Laughing, Dervish pats Shark on the back, points him towards the open mouth and guides him out of the maw of the monster, away from the gnashing teeth of the furious furry creatures, into the empty depths of darkest, coldest space.

Floating, the monster having drifted on, we tell Shark about our adventures and theory that we're in a chess board-shaped universe of thirty-two different zones. He listens quietly, distracted, looking around twitchily. Sighs when we finish, then says softly, "Thanks for coming."

"We need you," Dervish says.

"For what?" Shark snorts. "You were doing fine without me. You figured this place out and dealt with it. All I did was stay where I had something solid underfoot. I thought that was going to be the rest of my life, that mouth and those demons. Part of me wanted to surrender and let them..."

He shivers, looking very different from the Shark I first met. The fight has drained him of much of his confidence and strength. I want to say something to make him feel better, but Dervish speaks before I can put my words together.

"I think Lord Loss knows you're the strongest of us. He wanted to break you, wear you down and kill you off, so you couldn't help Kernel. That's why he stuck you in the bleakest spot he could find and did all he could to destroy you. But he failed. You're alive. You survived where any other would have perished. So forget the self-pity. You had it tough, you dealt with it - now move on, soldier."

Shark laughs. "Nice speech."

"But true," Dervish adds.

"Maybe." Shark's laugh turns to a chuckle. "I guess I'm not cut out to suffer nobly, am I?"

"No. You've had your few minutes of moping - now put them behind you and let's work on getting out of this place and finding that bar you mentioned."

Shark grunts and faces me, recovering in the blink of an eye. I wish I had skin as thick as his, that I could go from the depths of despair to normality in the space of a few heartbeats. "Are those marbles still working?" he asks.

"I guess."

"Think you can use them to find this thief of yours?"

"Possibly."

"Then set the hounds loose, boy - it's time to kick demonic ass!"