'Don't knock it, Doctor,' Harry said. 'We want to go faster.'

'But we're already on maximum. The fans are driven from power cells so there's no fuel weight loss, and the lift can only reduce as we get higher and the air thins. Which means either '

Max stopped trembling. 'Interference has ceased,' he reported.

In lab three the guard commander got to his feet, face blackened and ears still ringing from the explosion as the force field collapsed. There was a smoking crater on the bench where the Doctor's machine had rested. As Cara looked in dismay at her half-ruined laboratory, the commander put his wrist communicator to his lips. 'Device deactivated, Director.'

Down on the plain the synthonic tanks ceased their wild perambulations. Gun barrels and missile tubes swivelled round to re-acquire their target.

They were at the top of the cliff and Sarah once again told herself not to look at the ground a vertiginous mile below.

Before them the rocks shelved in a series of receding razor-back ridges, beyond which the blue sky merged with a bank of low cloud. The skimmer angled forward and crossed over the first ridge as brilliant needles of light cut the air behind them, blasting rock into vapour. But they were out of the line of sight. A slim missile arced out of the Valley and bore down on them. Max's gun arm moved more swiftly than any human or Jand reflexes could have animated it, and a bolt of fire met the incoming missile squarely while it was still fifty yards short.

The shockwave sent them reeling through the air as metal spanged against the skimmer's sides.

'I say good shot!' exclaimed Harry.

The skimmer rocked and Sarah became aware of an unpleasant grating vibration under her feet.

'Shrapnel must have hit a fan blade,' said the Doctor.

'Going down.'

Rocks rushed up towards them, projecting out of the cloud wreaths like black teeth. At the last moment the Doctor banked and they slipped through a gap between two peaks.

Beyond was nothing but blue shading into grey, and the sun was a fading orange ball behind them. Then it vanished completely and there was only chill damp cloud.

'We've done it!' said Ch.e.l.l.

'As long as we can see to land,' said the Doctor. 'Are your eyes better than mine, Max? Perhaps you'd better take us down.'

'Yes, Doctor. I shall emergency: brace for collision!'

Sarah had a fleeting impression of a vast blue wall in front of them, then there was an unreasonably solid impact. Sarah was catapulted forward and struck her head on Max's hard shoulder plate.

Fans whirring fitfully, holding them tight to the impossible wall, they began to slide inexorably into the grey depths below, accompanied by a long grinding screech of metal against stone.

How careless of us to b.u.mp our heads on the sky, Sarah thought dizzily, then pa.s.sed out.

22.

Out of Time arah came to her senses again coughing; a pungent odour Sfilled her nostrils.

Harry withdrew the capsule he had broken under her nose.

'Feeling better, old girl?'

'This is getting to be a habit,' she groaned. 'Oh, my head.

What happened? I have the oddest feeling that we ' She paused, blinking into the murky grey gloom and aware of heavy dank air pressing in around her. The Doctor, Max and the Jand were close by, the soldiers holding their weapons at the ready. Beyond them were the remains of their skimmer, which was resting at the bottom of a vertical striated trail gouged into an unbroken wall of blue that rose sheerly until it vanished into the fog-like haze. Far above was a pale strip of glowing cloud running parallel with the line of the wall. 'We really hit the sky?'

'Bit of a facer, isn't it?' agreed Harry.

They were at the bottom of what appeared to be a mist-filled valley dripping with condensation. The water collected into channels cut in the curving valley floor, which in turn fed a river that ran along its centre and vanished into the gloom on either side. From the symmetry of the lines it was obvious the entire construction was artificial.

'But what is all this?' she said, trying to sit up and wincing.

'The Doctor thinks it's part of the air-conditioning system for the Valley proper, so to speak fortunately for us it's not as deep as the other side. A condensation trap for the clouds, running right round the inner valley, which recycles the water to feed the mountain streams, and so forth.'

'Then Deepcity, this whole place, is really '

'Inside a large cavern with a domed roof several miles high, hollowed out of an asteroid,' said the Doctor, stepping over and squatting down beside her. 'How are you feeling now?'

'Confused. The world made more sense when I was unconscious. Everything in the Valley seemed so convincing.

And if this is an asteroid, why don't we feel as light as feathers?'

'They must have used some method of collapsing the excavated material into stabilized neutronium and plating the cavern floor with a carefully graduated layer of it to provide the illusion of normal gravitation,' the Doctor explained. 'But the effect is very localized and it diminishes far more sharply as you ascend than it would on a real world.'

'Which was why the skimmer speeded up,' said Harry.

'Exactly. And the air doesn't thin as rapidly as it should either. Then you only need a few extra tr.i.m.m.i.n.gs to make the illusion complete. Somewhere around here will be the rails on which the "sun" rides, and the projectors that produce the "stars" at night, and '

Sarah clutched her head again. 'Doctor, please enough.

Just explain why they went to all this trouble.'

'It's a very good hiding place for something you want to keep secret, of course. And Deepcity is very, very secret indeed,' he added with sinister solemnity.

'It also makes it a very hard place to escape from,' Harry pointed out. 'I don't see the Oranos Oranos burrowing through a few miles of rock to pick us up from here. Brant was right: the only way out is the s.p.a.ceport, and you can bet that's pretty well guarded by now. Pity we haven't got the TARDIS with us.' burrowing through a few miles of rock to pick us up from here. Brant was right: the only way out is the s.p.a.ceport, and you can bet that's pretty well guarded by now. Pity we haven't got the TARDIS with us.'

The Doctor stared at him, eyes wide, mouth open slightly, as though startled. 'Say that again, Harry,' he said faintly.

'Er, it's a pity we haven't got the TARDIS with '

'TARDIS!' The Doctor shouted so loudly that echoes returned from the far wall of the valley. ' That's That's the word I was trying to remember all this time!' He clapped his palms to the sides of his head. 'Turn it on its head the key the last piece the word I was trying to remember all this time!' He clapped his palms to the sides of his head. 'Turn it on its head the key the last piece

it all makes sense now.'

'Doctor, are you feeling quite well?' Harry asked anxiously.

He turned a brilliant beaming face to them. 'My dear Harry, I am feeling perfectly fine, thank you. Now I know what actually happened to us before we got here and where we've got to make for next. Are you up to moving, Sarah?'

With an arm from Harry she got to her feet. 'I think so.'

'Right, come on then.' The Doctor strode away, suddenly so full of renewed energy and purpose that he threatened to leave them all in his wake. 'Dekkilander Ch.e.l.l'lak we've got to cross the river.' They set off down the slope through the mist. Fortunately the river was shallow, sluggish and easily forded. On the other side the Doctor set them searching along the inner wall of the artificial valley. 'There must be inspection hatches somewhere. We'll use one to get inside the secret half of the complex.'

As they spread out, straining their eyes in the gloom, Sarah caught up with the Doctor again. 'But why pretend Deepcity is not what it really is on the inside? Who were they trying to fool?'

'The civilian scientists and technicians, I should think. I sense a security-obsessed politico-military mindset behind it, at least at the beginning. Deepcity was planned to be self-sufficient and self-contained, and they realized it only required a little more effort to make it a convincing illusion of a valley on the surface of a real world. There was a war on and security demanded the fewer people who knew the location of the base the better. What they didn't know they couldn't tell. Even if somebody was determined to give it away, false star patterns in a false sky would have them looking for a non-existent world in totally the wrong places. The security, maintenance and support staff would have to know, of course, but perhaps even they wouldn't know the whole truth. Because somewhere along the line its purpose has been perverted. But to what ultimate end? Who knows the whole story and who really runs Deepcity?'

'I detect activity ahead,' Max warned them.

'Everybody down here,' said Ch.e.l.l.

They crouched down in one of the drainage channels that fed the river. From out of the mist ahead came the clang of metal on metal, and the sc.r.a.pe of several pairs of heavy boots.

Then a distant voice: '...probably smashed themselves up flying over the edge.'

'Probably. But we find the bodies anyway, Pascal every one of them must be accounted for.'

'Yes, Chief.'

'You take Hensall and Crietz that way. Naversen and Backley, come with me. And remember they had a synth trooper with them it might still be functioning.'

'Yes, Chief.'

One group of boots receded, the other started towards them.

Ch.e.l.l waited patiently in the culvert until Sarah could hear every c.h.i.n.k of gravel and squeak of boot fastenings. Then he stood quickly, gun pointing meaningfully, and they all rose beside him mirroring his stance. 'Drop your weapons or we fire!'

The three Deepcity patrolmen, taken by surprise and facing six guns, had little choice. The Doctor raised his hat to the officer in charge. 'Ah Captain Morven. So considerate of you to come looking for us.'

Five minutes later they were climbing up the inset ladder that led to an access hatchway, leaving the security detail bound and gagged in a culvert. The Doctor closed the hatch behind them, then led the way along a rough-floored tunnel that angled into the depths of the cliff in which Deepcity was buried.

'What is our objective, Doctor?' Ch.e.l.l asked softly as they proceeded. 'The s.p.a.ceport?'

'No. As Harry said earlier it's bound to be guarded.'

'Maybe we should have tried to signal the Oranos Oranos while we were beyond the Valley's shielding. At least let them know what we have discovered.' while we were beyond the Valley's shielding. At least let them know what we have discovered.'

'It's likely the shielding extends over the condensation channel as well, and don't forget there's also a lot of rock between you and open s.p.a.ce. Anyway, what good would it do pa.s.sing on what we've learnt so far? We haven't any proof'

'What? My crew are witnesses to the freighter from Averon, and with what you've told me '

'Your witnesses are, as they will point out, an interfering alien and his two unreliable friends, a boatload of renegade Jand, all telling an improbable story of a link between Landor and Averon for which there is no hard proof. Even if the Landorans let you speak out, who'd believe you?'

'There are some in my government who will accept my unsupported word,' Ch.e.l.l said stiffly.

'At the risk of having your supplies of synthonic weapons cut off by Landor?'

Ch.e.l.l relapsed into thoughtful silence and they continued on, the Doctor leading them briskly and unerringly through a maze of service corridors, only pausing to let unsuspecting environmental engineers and simple track-mounted maintenance robots pa.s.s. Sarah knew their greatest strength still lay in their presence going undetected. But there was a clock ticking away. As soon as those men in the cloud trench were found the alarm would be raised again.

'Doctor where are are we going?' Sarah asked at length. we going?' Sarah asked at length.

'A junction point between the secret half of the complex and the rest, located near to a certain store-room in the laboratory section. I noticed a map of the concealed doors on the wall of the sub-level file room last night just before my investigations were rather rudely interrupted.'

'Just "noticed",' Ch.e.l.l asked. 'And you remember the way exactly?'

'Of course. I must have looked at it for at least eight seconds.'

Ch.e.l.l was silent again.

'And what do we do when we get to this store-room?'

Harry asked.

'We leave, of course.'

'Just like that?'

'Hopefully we haven't the force to do anything more and I think we've outstayed our welcome. But we'll be back.'

'Footsteps,' Max warned.

They flattened against the wall as a couple of men in overalls walked unconcernedly across the junction at the end of the corridor. The Doctor moved ahead, peered down the way they had gone, then waved the others on. Around the corner was a large section of pipework with a man-sized hatch set in it, which ran vertically from floor to ceiling and presumably formed part of the ventilation system. The Doctor unlatched it, revealing hooped rungs bolted to the inside leading upward. 'This is it. The hatch at the top opens into the upper complex. I'll go up first and attend to the lock. Harry, will you come last and make certain this hatch is properly closed behind us?'

'Right ho, Doctor.'

They began their ascent.