He had a faint memory of struggling into semi-consciousness just after the ambush. One of the moth-like creatures had bent down to bite him. The mandibles had opened and a needle-like probe had extended, dripping poison. He remembered the creature's head moving away, its leaf-like antennae quivering, and then everything became dark again.

Some time later the Doctor had recovered consciousness, his neck feeling tender and swollen. The knights appeared to be out cold, each one draped over the shoulder of a moth, carried deep into the darkness.

For the moment the Doctor tried not to think too hard about the creatures, nor what they had planned for their prey. Slowed down by their prisoners, the moth-men trudged along the stone and metal corridors, wings hanging idly at their backs. The Doctor wrinkled his nose at the smell that rose from the creatures' oozing, creaking joints.

He twisted his head slightly to one side, keeping his eyes half-closed for fear of discovery, and stared intently at the walls and buildings that they pa.s.sed.

With an involuntary twitch he realized exactly what his eyes had been telling him for so long. Rough natural caves and crude sewer pipes of stone had been replaced by buildings, thoroughfares, suites and corridors of soft metal alloys and mock wood.

The old city - for that was where they now were - was technologically advanced and well preserved, having idled its time in dusty amber for centuries. The Doctor glimpsed broken street lamps and carefully parked hover-cars, large recreation areas and fortified bunkers surrounded by crumbling razor wire.

So, this was the source of the diverse civilizations that now sprawled across the planet. Once the people had left the city it had been built upon and forgotten, until now its very existence had become the stuff of speculation and legend.

The Doctor marvelled at what deceptive progress mankind and nature could achieve over a millennium or three.

And yet the lines of the place, its austere minimalism, worried the Doctor. This was no neglected colony, but neither was it a harsh penal inst.i.tute or correction centre. Its very form, and the frequency of the bunkers and rusted military vehicles, hinted at a hawkish conformity, balanced by occasional concessions to comfort and the needs of the family.

As this thought pa.s.sed through the Doctor's mind the spiny foot of the creature that carried him stamped down on a toy ark, upended in a gutter choked with dust and dirt. The wood, made brittle by the pa.s.sing of time, splintered, spilling out a few plastic animals.

The Doctor had previously thought that the Menagerie of Ukkazaal, if it existed at all, would perhaps be the underground city's zoo. He had expected to find little more than the faintest impression of old corpses, still locked within sorry cages and cracked vivaria. But the very existence of these moth-creatures indicated that large numbers of animals had existed here, enough to found a b.e.s.t.i.a.l civilization of their own. And the fact that the city was so clearly a military research area was more worrying still.

What had caused the humans to leave this place? Was it biological warfare, nuclear radiation, or something more mundane? Perhaps a period of galactic contraction had left them stranded without supplies. Perhaps some war had spilled over on to the planet's surface, with most of the population taken away as prisoners or executed and thrown into ma.s.s graves.

The Doctor was puzzled by the twilight that gently coloured in the outline of the buildings and streets. Surely, this far below ground, everything should be dark. Either there was some fissure that let in a glint of the surface's dull grey light or . . . The Doctor craned his head around slowly, trying to ascertain the light's source.

Eventually he saw it. A mile or so in the distance was an unremarkable squat building, a few radio masts and chimneys gathered together at its rear. Uniquely among the buildings of the old city its rooms and doorways spilled yellow light, although the Doctor could detect no figures within. Its lights cast little slivers of brightness through the gloom and up towards the artificial sky half a mile or so above his head. Whoever was breathing life back into the machinery and buildings of the city had no idea of the potential dangers.

The moths on the other hand seemed to be quite content in the dark and, indeed, they were moving in a direction that took them far away from the building. The construction shrank slowly into the distance, a single candle slowly snuffed out in a black and stifling h.e.l.l.

Araboam locked the door carefully and kicked off his boots. All the while the young woman watched him carefully. She smiled as he turned to her. 'I thought the knights' thoughts were always on the Higher,' said Kaquaan.

'Maybe,' grunted the knight. 'But sometimes we feel the call of our baser instincts. Sometimes I think we are not more civilized than the bulls and cows I watched in the fields when I was young.'

'Situation has meant that I rely on such instincts,' said Kaquaan.

'I'll make sure you're paid,' said Araboam harshly. 'Think of me when you repent and beat the evil out of yourself.'

'I'm sure I will.'

Kaquaan watched as the knight began to pull off his armour, making a neat pile of metal and leather towards the bottom of the small bed. The rest of the room was bare and unremarkable. A few esoteric symbols had been crudely carved into the stone wall, and the roof was covered by a tapestry of the night sky's stars set into a globe and held gently in a pair of great, pale hands. There was little to distract her.

She strode over to the knight, smiling. 'I'm glad my lord does not find my shaven head too ugly.'

'Whoever did this to you had some sense.' Araboam stroked her cheek with his hand. ''Tis a suitable punishment for a wh.o.r.e. And it is not your face that I am interested in.'

He reached out and squeezed her b.r.e.a.s.t.s, smiling appreciatively. 'Not bad,' he said, as if commenting on livestock.

'I'm glad I please my lord,' whispered Kaquaan, averting her gaze. 'I can think of many more ways to bring you pleasure.'

'Good,' breathed the knight, beginning to tug at her coa.r.s.e blouse.

'And none more exciting than this.' With that, she thrust her knee hard into his unprotected groin. The man collapsed with a shocked moan.

She grappled for the man's huge helmet, and swung it at his head. It took a number of unsuccessful attempts before she managed to club the unresisting knight into unconsciousness. Eventually her hands came away speckled with blood and hair.

She took the knight's sword and keys and carefully unlocked the door. She checked that the corridor beyond the sleeping chamber was deserted, locked the door behind her, and then fled into the shadows.

Diseaeda stood at Zoe's side, tears rolling down his cheeks. 'What can we do?' he whispered.

From their vantage point towards the rear of the tent they could watch the creature in action. It was tremendously strong and quick, darting from group to group, slashing with its four arms, snapping with its gaping maw. It blurred and came straight through tent walls and people, turned on frightened animals and ripped them in two. Its original colouring was lost now under a thick film of brown blood, and it turned its head at every new sound, every scream.

One of the animal trainers, knocked to the ground by a falling caravan, tried to struggle to his feet. The creature swung its head lazily in his direction and, ignoring the monkeys that screamed and dived for cover, extended one arm towards him, secured the man's neck in a serrated vice-like grip, and squeezed.

Zoe swallowed down her bile. 'I'm not sure what we can do,' she said quietly. 'The monster is clearly not killing for food or for any other purpose. Its aim is to kill all living creatures.'

'Can we hide from it?' asked Raitak.

Zoe turned her face away from the carnage. She had just watched a man seeking refuge behind what appeared to be a chess-playing automaton, but the creature stalked over in his direction regardless. It forced a claw straight through the device, and lifted the man to its smooth snout, staring at the creature quizzically through concealed eyes. Zoe hadn't wanted to see the rest. 'It seems to be hunting as much by sound as by sight,' she speculated. 'Unless . . .' She paused in thought. 'Perhaps it's tracking its prey in a different way.

Get me a torch.'

'A what?' said Diseaeda. His voice sounded slurred with shock. 'Why do you -'

'Just do it,' she hissed.

Diseaeda slipped into the tent.

The creature paused for a moment, as if to survey its surroundings and to watch the people that streamed away in every direction. When Zoe had first seen the creature fathers had rushed to protect their families and had been torn in two. One of the strongmen, a mountainous figure fully twice Zoe's size, had been battered to the ground and left like a broken toy.

By now, people had recognized what they were up against. This was no game, no part of Diseaeda's freak show. The blood was real, the slaughter enormous, and the thing seemed to be only just getting into its stride. It leapt on to the top of another small tent and forced it to the ground, spilling conjuring tricks and magic boxes. It stared up into the sky and, just for a moment, brayed at the wind. It was a laughing expression of satisfaction.

Diseaeda returned with one of the flaming torches used by the jugglers. Immediately the creature's head turned in their direction.

'Ah,' said Zoe. 'A good experiment, but rather too successful. The creature appears to like the torch.'

The animal clambered down off the wreckage of cloth and wood and stalked towards them, its movements slow and playful.

'So?' asked Reisaz, as they retreated back into the now deserted main tent.

'So,' said Zoe, 'its vision might be biased towards the infrared end of the spectrum. This primitive device gives off more energy in heat than in light.'

'And?' asked Diseaeda as they worked their way through the backstage area.

And heat is common to all living things, and it's very difficult to disguise.'

The creature ripped into the tent just as Zoe and the others reached the centre of the circus ring.

'Which means, very simply,' continued Zoe, 'that we can't hide.'

After a grim journey in complete darkness the Doctor sensed that they were now in the creatures' more usual surroundings. Sound was m.u.f.fled and dull, the air musty, reminding him faintly of an animal house at a zoo.

The Doctor was thrown to the floor. There was great activity around him as he was dragged roughly across the ground. The Doctor tried not to cry out. Something soft but very strong wrapped around his feet. Then his knees were bound together.

With a sudden dizzying rush the Doctor's feet were hauled upwards, his face now swinging above the ground, although he could see nothing.

It was then that he realized that he was being coc.o.o.ned.

Zoe, Diseaeda and the twins fled across the ring, sawdust flying high into the air. They dared not turn to watch the progress of their pursuer, although the sound of its claws as it paced after them was clear enough.

'We need,' panted Zoe, 'to get somewhere hot. That might interfere with its infrared vision.'

'I can't think of anything,' said Diseaeda, holding his chest and beginning to slow already. 'Perhaps if I sacrifice myself to the creature it'll give you all the chance to escape.'

'Diseaeda,' hissed Raitak. 'Concentrate on running.'

'Leave the thinking to Madam Zoe,' said Reisaz. 'Besides, you'd be barely a mouthful.'

Zoe glanced behind and saw the creature stalking after them, following them down the canvas-covered tunnel that led to the tent's main entrance. It could have caught them by now if it had really wanted to. She could only imagine that it was playing with them, waiting for their exhausted bodies to collapse or trip. She hoped that the creature's enormous, brutal confidence would be its undoing.

'What's the biggest animal in the circus?' she asked.

'The savannah walker,' said Raitak as they ran across the rain-sodden turf of the circus site.

The creature stepped out of the tent and lunged at a terrified horse that ran past. The animal's head blurred as the neck twisted and snapped. Only the horse's momentum carried it forwards but by the time it crashed into the earth in a ma.s.s of splayed legs it was very still.

The creature jumped on the horse's back, checking that it was dead, and then set off again after the torchlight.

'I have an idea,' said Zoe. 'Which direction is the savannah walker?'

Diseaeda stabbed a blunt finger towards a collection of temporary animal houses towards the edge of the site. They started to run in that direction, rounding trailers, jumping over tent ropes, all the while screaming warnings to the people that pa.s.sed them by.

Some of the men and women they watched were almost motionless with shock, their lips quivering, their eyes glazed over at the butchery they had witnessed. Others ran crazily in different directions, senseless with fear and numbed by the desire to survive. Those with slightly cooler heads had gone towards the town, seeking help.

'Let's hope we get there before this thing gets bored with the chase,' said Zoe.

Jamie tried to rest but found that the bunk-like bed in the cell offered little encouragement. His mind turned over and over the fate of his friends, Cosmae and the girl. With every minute that pa.s.sed his subconscious painted more and more gruesome images behind his closed eyes.

He thumped the bunk in frustration, trying to block out the nightmarish reflections. He had to admit it: despite all his adventures with the Doctor, even in this society he was well out of his depth. Whatever had happened to him previous to waking up in the young knight's office - and his memories were no more clear than a watercolour landscape awash with rain - had left him feeling helpless and unsure. Even now he could feel things moving in his mind. It was as if his memories were items of furniture and a huge hand was dragging them experimentally across floorboards and into new positions.

His head began to pound. He pressed his fingers into his temples, groaning.

The banging got worse, followed by a crash that made him wince.

He pushed himself into a sitting position and saw that the door to his cell had been pushed open. The young woman, Kaquaan, stood framed in its light, jangling a large bunch of keys.

'Come on!' she said, handing Jamie a huge sword. 'The jailor will not sleep for ever.'

'My brave wee la.s.sie!' exclaimed Jamie, jumping to his feet and immediately feeling much better. 'I'm forever in your debt.'

'It was easy,' said the girl. 'In most cases the knights haven't been with a woman for years. I don't care how much you pray to the Higher, there are certain . . . services . . . that I can offer that no man can resist.'

Jamie wiped a sudden trickle of sweat from his brow.

'When I was a bairn I was warned about people like you.'

The girl smiled. 'Put your boots on, and let's go.'

'Aye,' whispered Jamie to himself. 'She's a pawky one, and no mistake.'

The Doctor had been in more difficult situations, but for the moment he was hard pushed to think of one. His eyes had become fully accustomed to the dark, and the faint natural luminescence of the cave walls indicated the graphic nature of his predicament. He and the other knights, still comatose from the moth-men's poison, were suspended and entrapped in huge woven coc.o.o.ns, hung from the ceiling on strands of silk as strong as steel cable. Only the Doctor's head was free, allowing him to breath.

The small cave, therefore, was nothing more than a larder, a grotesque pantry of living things. At least, that's what he hoped the cave was. The only other thing he could imagine - that they were all being stored prior to implantation of eggs - was even more grotesque. It was little wonder that he had always found entomology so faintly disquieting.

The Doctor had noted that one of the knights was missing. How had he managed to escape from such powerful creatures? Perhaps he had been allowed to escape, in which case the moths were simply following orders so as to spread terror. But whose orders? The Doctor gloomily concluded that the one knight at liberty would not be able to save the others from the moth-men. He probably wouldn't even know where his fellow knights and the Doctor had been taken.

The Doctor was aware of a slight scuffling sound behind him. He began to rock gently backwards and forwards against the coc.o.o.n, inclining his head slightly. A few moments later he had turned sufficiently to allow him a view of the source of the noise. He could just make out a small pair of legs and a slim body, eyes that twinkled in the dark and a long, twitching nose like that of a shrew. Hands on hips and upside down from the Doctor's point of view, the creature stared at him through the darkness.