He watched Sam's reaction out of the corner of his eye. 'This controls the biodata around here?'

'Not exactly. The ReVit Zone was designed by humans, and humans didn't build this. The machine was planted here by someone else. Someone who wanted to protect their property.'

'Then this thing controls the leopards?'

'And the insects.' The forest kept growling. The Doctor wondered if he'd see a big cat standing in the entrance if he turned around. He made the point academic by not turning round. 'As soon as we stepped out of the TARDIS, I was bitten by something. So were you. If I know my biotechnology, the insects are programmed to take biodata samples from anyone who gets too close. If they decide the visitor's friendly, all's well and good. If not, they call out the guards.' But who'd use a security system this complicated, he wondered, and who were they trying to impress? 'This machine contains biodata samples from everyone who's authorised to be here,' he concluded.

'You mean, like a guest list?'

'Like a guest list. Ah.' The Doctor's fingers touched liquid, brushed the surface of a tiny reservoir deep inside the guts of the machine. A fluid bio-array, then. Perfect. The substance was sticky and rippled expectantly beneath his fingertips. 'Give me your hand.'

'Why?' said Sam. So he ignored her, grabbed her hand anyway, and locked it between his fingers. 'Ow,' she said, as he thrust both his hand and hers into the bio-array.

There was a moment of sheer bodily confusion, as the Doctor forgot exactly who he was and what he was doing. A side-effect of coming into contact with the array, he reasoned. He was becoming part of it, and it was trying to become part of him, trying to force its data into his biosystem. He denied it access, and told it to stay off Sam, as well. The bio-array obliged. It knew better than to argue with a life-form like him.

The Doctor withdrew his hand, and let go of Sam. His fingers weren't even wet. The array had backed down, and now it was keeping itself to itself.

Sam made a sudden gasping sound.

The Doctor turned. One of the panthers was standing at the threshold of the building, its musculature practically filling the archway. Though its body looked tense, there was a faintly bewildered look on its face, as if it had been in the process of doing something important, but had forgotten exactly what.

The Doctor stepped forward. The animal didn't react. He kept walking, until he was right in front of the creature, then reached out for its face.

After a moment's thought, the panther started licking his fingers. The Doctor smiled.

'We're on the guest list,' he said.

Mr Qixotl waddled along the pa.s.sageway at full tilt, wondering if he'd be able to retain that dignified, professional air even when things were falling apart around his ears. Not that anything had gone wrong, as such. The "property" was safe, Homunculette hadn't got round to physically a.s.saulting him, and everything was going according to schedule.

From the point of view of diplomacy, though, things could have been better.

The humans had turned up at the ziggurat. Two of them, both from UNISYC. Mr Qixotl had been so busy arguing with Homunculette, he hadn't even noticed their arrival until he'd run into the man Kortez, his name was in one of the tunnels between the entrance and the conference hall. The trouble was, the man had left the other human rep back in the main corridor, and by the time Mr Qixotl had reached her she'd already stumbled across the guest rooms. At least, she'd stumbled across Trask's guest room. The girl had been at the ziggurat entrance when Qixotl had found her, retching her guts out.

He'd hustled the two humans into the c.o.c.ktail lounge, the female looking decidedly green around the glands. He'd left them there with a complimentary bottle of something he didn't think they'd find too toxic, saying he'd formally introduce them to the others soon, and a.s.suring Kortez that yes, actually, the chairs were exactly what they seemed.

Mr Qixotl skidded to a halt in the guestroom corridor. Yeah, OK, so maybe the human woman had a point. Trask wasn't an easy ent.i.ty to deal with, not by anyone's standards. Homunculette looked the same as any other humanoid, and you even got used to the Shift, after a while. Trask, though... it wasn't as if there was anything physically wrong with the man, as such. If you saw a photo of him, you'd think he was perfectly normal. It was only when you saw him, in the flesh, that you realised.

The signals he gave off. The zombie body language. He didn't move like a living thing. Mainly because he wasn't wasn't a living thing. a living thing.

Mr Qixotl steeled himself, then walked up to the doorway of Trask's room.

'Afternoon, Mr T,' he said, trying to sound cheery. 'I hear you had a little visitor.'

Trask was sitting on the bed, a skeletal smile fixed on his face. The girl had said he'd been smiling, Qixotl remembered. He wondered if Trask had changed his facial expression since she'd been here.

'Yes,' said Trask. 'This room has no door.'

His voice, like his face, had absolutely no trace of life in it. Qixotl had to concentrate just to figure out what the words he said actually meant. 'Yeah. Sorry about that. Design oversight. Not too much of a problem, I hope?'

'No. Mr Qixotl?'

'Erm, yeah?'

'I want to speak to you. In private.'

Something turned in Qixotl's stomach. 'Bit on the busy side right now, Mr T. Delegates turning up all over the place and everything. Maybe later on we can figure something out, yeah?'

'You know who I represent,' Trask creaked.

Mr Qixotl glanced around the room, hoping to find an excuse to end the conversation. Unsurprisingly, there wasn't one. Trask's room was bare, apart from the bunk. 'I know, Mr Trask, I know. Look, I won't tell any of the others, if that's what you're worried about. Discretion's a.s.sured, yeah? A lot of the other bidders haven't made their, er, their allegiances exactly public, if you follow me.'

'I want to make a deal.'

Qixotl stared at him. Then wished he hadn't. 'Well, yeah. I mean, you'll have your chance to make your bid '

'No. I want to make a deal. With you. Confidentially. Before the auction.'

'That's not exactly, y'know, regular,' said Mr Qixotl.

'I know,' said Trask.

There were a lot of guest rooms in the ziggurat. More, in fact, than would ever be needed. The lowest level was a veritable labyrinth of corridors, peppered with pseudo-stone chambers full of warm air and torchlight. There was absolutely no need for any more rooms to be added.

Nevertheless, a new doorway spontaneously appeared in the wall of one of the side-pa.s.sages, materialising with an ugly grating sound which according to one popular mythology, at least was the sound of Time itself groaning in agony. In defiance of the normal laws of spatial dimension, a new set of rooms appeared on the other side of the doorway.

After a while, two figures stepped out into the corridor, and stood there for a few moments, surveying their surroundings. The shorter of the two wore a Victorian funeral gown, heavy skirts sweeping the floor, a dark veil pulled across her face. The taller figure wore a suit, just as sombre in style. Not exactly elegant, but certainly formal. Ceremonial, even.

Beneath the woman's veil was a face of raw bone. The snout was sharp, the jaw was set into a permanent leer, and there were jagged holes on either side of the face, empty s.p.a.ces where the delicate mechanisms of the ears should have been. The features of a skeleton, the skull of an enormous bat. The man's face was, to all intents and purposes, identical.

The two figures locked arms, then turned, as one. They moved off along the corridor, at a pace that could only have been described as "relaxed".

Two more of Mr Qixotl's guests had arrived in the ziggurat.

3.

LOATHING THE ALIEN.

Every now and then, Sam found herself thinking of the Doctor as a set of responses, not a man half-man person person at all. Maybe, just maybe, that was the only way a poxy human mind like hers could come to terms with him. As an equation, rather than a living being. A function of the universe, whose purpose was to (a) break into places and (b) break out of them again. It didn't matter whether he was dealing with a cast-iron padlock or a bunch of genetically engineered toucans. Security devices would take one look at him and give up. at all. Maybe, just maybe, that was the only way a poxy human mind like hers could come to terms with him. As an equation, rather than a living being. A function of the universe, whose purpose was to (a) break into places and (b) break out of them again. It didn't matter whether he was dealing with a cast-iron padlock or a bunch of genetically engineered toucans. Security devices would take one look at him and give up.

The wall of the "Lost City" hadn't been far from the outhouse where the Doctor had found the biodata machine. He'd strolled right through the City archway without a second thought, head in the air, hands behind his back. He'd made straight for the central pyramid, sniffing disdainfully at the smaller buildings around it. 'Shoddy workmanship,' he'd mumbled, more than once.

They were inside the pyramid now. Sam had seen a lot of corridors over the last few months, but the pa.s.sages here were something new. No vent shafts or strip lighting, for a start. Lots of quivering shadows, lots of flickering torches. More like the cloister room of the TARDIS than, say, the connecting tunnels on board the Quetzel Quetzel. These corridors were more...

'Corridory,' Sam suggested, accidentally saying it out loud.

A couple of metres ahead of her, the Doctor stopped at a three-way junction. He seemed to have heard her, for once.

'Yes, they are, aren't they?' he muttered. He surveyed the junction for a moment or two, then licked his finger and held it in the air. 'Purity of architecture. Most corridors are built to be functional, but this one's supposed to give the impression of being being a corridor, judging by the feel of it. Are you psychic, at all?' a corridor, judging by the feel of it. Are you psychic, at all?'

Sam suddenly realised the Doctor had turned to face her. She saw big blue-green eyes in the half-light. Staring, not bothering to blink. You could tell, by the look on his face, that the Doctor thought his eyes were full of madness and poetry.

They weren't, though. In a previous life, this had probably been his best hypnotising stare, but his face was built differently now. Sam knew all about the Doctor's previous lives, the other bodies he'd lived in and lost over the years. She also knew that "this" Doctor, "her" Doctor, still didn't really understand what he looked like, or appreciate the impression he left on the rest of the universe. How long had he been walking around like this? Three years, by his reckoning? And he hadn't figured out who he was yet.

Just for a second, she felt sorry for him. Because he wanted to be a force of nature again, he wanted to be the incredible escaping equation all the time, but instead he was trapped in a half-human body with a baby-face and floppy curls.

'Psychic?' Sam queried.

The Doctor broke off the stare. 'There's something here. Something trying to make contact. I can almost feel...' He punctuated the sentence by jumping up and down. Testing the gravity, maybe. 'Beneath our feet. Something beneath our feet. Throwing out tendrils.'

'OK, let me try and translate this into English. Somebody in this pyramid's trying to make psychic contact with you, is that what you're saying?'

'It's not a pyramid. It's a ziggurat.' A new expression materialised on his face. It took Sam a few moments to identify it as a look of pure hurt. Like a child whose parents had just told him that he smelled. 'It doesn't want to talk to me. Every time it comes close, it pulls away. It's trying to make contact, but it's...'

The sentence ended in mid-pontification. The Doctor moved, faster than Sam could follow. With one smooth motion, he turned, and leapt back down the pa.s.sageway towards her. A second later, he was standing with his back pressed against the corridor wall, pulling Sam towards him. His hand was clamped across her mouth before she'd even managed to open it.

There was a second or two of absolute silence. Then there were footsteps. Human footsteps, by the sound of them. Around the corner. Getting closer.

Two figures walked past the corridor where Sam and the Doctor stood, moving across the mouth of the t-junction. Sam watched them go by, but the figures didn't even glance in her direction. The torchlight turned the two newcomers into smudges of orange and black. Sam tried to focus on the contours of their clothes, the details of their faces...

She hiccuped. Somehow, she managed to do it silently.

Eventually, the figures disappeared along the tunnel. The Doctor held Sam still for another minute or so, making sure the coast was clear before he let her go. Sam started spitting as soon as she was free of him.

'Yeuch,' she said.

The Doctor nodded. 'Yes. They weren't very attractive, were they?'

'I was talking about your hand. Do all Time Lords taste of chicken, or is it just you?'

The Doctor paused for a second, as if considering sticking one of his forgers into his mouth to test it, then frowned. 'Now is not the time, Sam.'

'Yeah, I know. Those two. I thought they were human, but...'

'But?'

'They didn't have faces. Skulls. They had bare skulls. Not human skulls, either.'

The Doctor looked pensive. 'Half-human, half-bat. How did they make you feel?'

G.o.d, it was a h.e.l.l of a day for questions. 'Well, they were kind of... I don't know. They didn't make me feel anything, much. Oh, right. I think I know what you're getting at. Every time I've been near an alien so far, I've been able to feel it. Like there was something different about them. Present company not excepted.' The Doctor looked indignant, much to Sam's satisfaction. 'But those two didn't make me feel anything. They might as well have been a couple of people in masks. Right?'

The Doctor peered along the tunnel after the skull-people. 'They were were a couple of people in masks. The Faction recruits agents from all sorts of races.' He wriggled his shoulders, feigning a shudder. 'I'm still picking up biodata traces. More intense than usual. Being in contact with that machine must have heightened my senses.' a couple of people in masks. The Faction recruits agents from all sorts of races.' He wriggled his shoulders, feigning a shudder. 'I'm still picking up biodata traces. More intense than usual. Being in contact with that machine must have heightened my senses.'

'The Faction?'

The Doctor seemed suddenly irritated, as if the thrill of explaining things to stupid humans had finally worn thin. He reached into his jacket. 'Faction Paradox. It's a family affair.'

'A what?'

A book emerged from the arcane depths of the Doctor's inside jacket pocket. It was a small paperback, and it looked as though it had spent the last couple of centuries hanging around in a loft somewhere. His eyes still fixed on the pa.s.sage, the Doctor pressed it into Sam's outstretched hands, although Sam was sure her hands hadn't been outstretched the last time she'd checked. Strange thing number eighty-nine, she decided.

The cover of the book was black, marked with hundreds of tiny white wrinkles and speckled with cartoonish drawings of galactic spirals. Or were they swirls of DNA? Whatever. Splashed across the cover, in blocky white letters that might have been used for the t.i.tles of a biblical epic starring Charlton Heston, were the words GENETIC POLITICS BEYOND THE THIRD ZONE. Under that was the author's name GUSTOUS R THRIPSTED and, in smaller letters, the words HARDCOPY POCKET EDITION. A dead wasp was stuck to the spine.

Sam flicked through the yellowed pages. Yellowed by spilt coffee, she guessed, not age. There was no sign of an index, but the corner of one page was turned down, close to the end of the book. She skim-read some of the text there. Not an easy task, in this light.

Even in primitive cultures, where temporal physics is considered to be little more than science fiction, people are aware of the problems time travel can cause. Perhaps the most famous of all the fourdimensional conundrums is the so-called "Grandfather Paradox". Suppose, goes the argument, I were to travel into the past and murder my own grandfather, as a young man. If I did this, my father would never exist, and so logically neither would I. However, if I never existed, I could never have travelled back in time and murdered my grandfather. Hence, my father did did exist, and so I exist, and so I did did travel back in time and murder my grandfather... and so on and so forth. travel back in time and murder my grandfather... and so on and so forth.

But in time-active cultures such as that of the Time Lords, these paradoxes are more than mere fantasy. To them, the perils of time travel are harsh realities, and Time Lord folk stories are full of cautionary tales about characters who inadvertently murder their own ancestors, or disobedient children who break the First Law of Time (though there is some disagreement in Time Lord society as to what the First Law actually is). For Gallifreyans, the word "Paradox" has the same connotations that the word "Sethite" did for the ancient Osirans, or that the word "Satan" still does for many human tribes. "Paradox" is the greatest imaginable evil, the dark side of the time-travelling lifestyle, a horror never to be mentioned in polite society...

Paradox. As in, Faction Paradox. The folded page was an introduction to the Faction. Sam looked up, to ask the Doctor if this was pure coincidence, or if he'd planned it that way.

But the Doctor wasn't there. Sam scowled, and squinted into the gloom at the far end of the pa.s.sage. Halfway along it, she spotted a blur of green velvet, striding off into the depths of the ziggurat, apparently in pursuit of Mr and Mrs Bat-Head.

She glanced down at the book again.

Inevitably, there are those who have a morbid fascination with such evils. Just as the human race has sp.a.w.ned "Satan-worshippers", at least one group exists which has dedicated itself to the study of Paradox, turning its back on traditional Time Lord values and instead embracing a form of dark shamanic spiritualism. Indeed, this group is not unlike one of the voodoo cults of Mutter's Spiral, with its own pantheon of spirits and demons, and its own occult rituals. The group is known as Faction Paradox, and it's hard to describe the dread this name conjures up in the minds of the Time Lord archons...