'Get back, get back!' Ian shouted, waving his arm desperately.

Barbara had the sense not to argue. He saw her turn to run just as the entire roof caved in.

Ian twisted aside, slipped, fell to his knees and scrabbled awkwardly away from the wall of falling concrete. A slab, dislodged from the roof, smashed down on the pedacam as it scuttled along at his heels, flattening it in a brief shower of sparks.

Gradually the sound of falling rock diminished to a soft patter. Thirty yards clear of the fall Ian slumped against the wall, his heart pounding as he raged silently. Curton's voice was shouting from the earphones of his helmet radio but for a moment he ignored it. All he could think of, quite irrationally, was that they had tempted fate by joking about the irony of their situation. How could this have happened? They had been so close.

Then reason rea.s.serted itself. At least he knew Barbara was safe. Wearily he acknowledged Curton's call and explained what had happened.

'Is the tunnel completely blocked?' Curton asked.

'Yes.'

'Then you'd better get out of there quickly.'

'No. Send down your machines. We must get Barbara out.'

'Listen. It's still raining heavily. If the tunnel's blocked the water's going to he back up to the ceiling before we can get down there.'

Ian looked down at the swirling water and realised Curton was right. In a few minutes it would submerge the walkway.

'When the pressure builds up enough that plug will blow like the last one,' Curton continued. 'You get back to the Carlson Tower feeder as fast as you can while I open up the next access point downstream. I just hope your friend has the sense not to hang around.'

On the other side of the roof fall, Barbara was reluctantly coming to the same conclusion as Ian. The main channel was being filled by water flowing in from the side culverts, but she could already see small rivulets emerging from higher up the wall of rubble above it. It didn't take much imagination to guess what would happen when it collapsed. She had to get clear and hope Ian could find some way of reaching her further down the tunnel.

She headed back the way she had come, as fast as she could safely go on the newly soaked walkway.

At least Ian knew roughly where she was now, she consoled herself as she stumbled along. And that helmet and overalls he'd been wearing suggested he'd got some help from somewhere... presumably the place that the mechanical dog-thing running along in front of him had come from. Hopefully it meant that when she reached the nearest manhole ladder there would be somebody up there to unseal it this time.

Ian splashed through the water lapping over the edge of the walkway. Still the side culverts gushed with more. Allowing for the gradual fall of the tunnel, the section before the collapse must already be filled to the ceiling. The water would be backing up now, increasing the pressure as it rose. Would the temporary dam last long enough for Barbara to get clear?

He saw lights ahead that marked the mouth of the culvert through which he had entered. Panting for breath he reached the flexible ladder which hung down into the main tunnel. The water was swirling about his ankles as he started to climb.

Then from far down the tunnel he heard a faint booming sound. Even as he peered into the darkness he knew what had happened. The dam had burst.

Barbara heard the roar of water growing in volume like an oncoming express train and knew she would never reach the access shaft in time. If it caught her she would be smashed against the walls by its force even before she had time to drown.

With the terrifying sound filling her ears she looked about desperately for some kind of shelter. A few yards ahead of her on the other side was a smaller branch inlet, a pipe no more than five feet in diameter. She had ignored it during her first journey down the tunnel because it had no walkway. Now it might save her life.

She leapt into the water and splashed across into the mouth of the inlet, fighting the flow of its current. Finding her feet she managed to wade a few yards inside. But even though the pipe was only half-full its flow was too strong... or perhaps now she was too weak. Her feet were sliding over the bottom as she was pushed back towards the main tunnel and certain death. She dropped her torch and grabbed the sides of the pipe, raking her nails into the slime-encrusted walls, slowing her progress for a few vital seconds.

A foaming wall of water thundered through the main tunnel behind her.

Barbara's ears popped as the torrent compressed the air in the pipe like a piston. The water boiled and swelled under her as a part of the cascade exploded into its mouth. She was caught up by a wave that filled the pipe and carried her away into the darkness.

Prince Keldo Arrosthenos sat alone in his conference chamber and allowed himself the luxury of letting his thoughts run free for a few minutes. The end was so close now that he could almost taste victory.

A year ago it had been so very different.

When his flagship had been brought down on the beach just outside Arkhaven's walls, Keldo had expected to die. For three days the fires burnt in the outer hull, fed by exploding fuel and munitions, while he and his men fought to stay alive within the core decks, sustained by bottled air and pressure suits. Out of a crew of over fifteen hundred 132 survived.

Only on the fourth day did the fires diminish enough for them to cut their way through to the outside world.

They emerged ready to die fighting gloriously as befitted the last warriors of the Taklarian Empire.

But there were no Arkavians waiting for them, nor did the city batteries blast them to fragments, though they were helpless in their sights. Slowly the ironic truth dawned. The Arkavians believed they had all died in the crash. They had retreated behind their walls again to continue working on their escape Ship.

Keldo's force was safe while the Arkavians did not suspect their presence, but it was intolerable to look upon the brilliantly lit city and know they could do nothing to prevent the Ship launching without them. Even with the element of surprise, they were now too few in number and too ill-equipped to have any possible chance of taking it by direct a.s.sault. And no reinforcements would be coming to their aid.

Their homeland lay in ruins, pounded by moon storms, the lands they had overrun had degenerated into savage anarchy as the end approached, and now the imperial fleet was destroyed.

Though they searched across the radio frequencies they heard no signal of Taklarian origin. They might be the last of their race left alive.

But Keldo refused to accept defeat. It was a year before the moon would strike Sarath. With only a tenth of the original crew to support, the remaining rations could be made to last that long. Keldo consulted with old Thorken Menanius, the fleet scientist. Together they evolved a new plan of action.

They made the wrecked battlecraft habitable again, shielding its remaining operational reactor so their activities could not be detected from the city. They braced and sealed the inner compartments against the surge waves that rolled in from the sea and gradually buried the hulk in the sand even as they washed away the debris of battle.

Once their base was secure they commenced their clandestine a.s.sault on Arkhaven.

With improvised tools they began cutting a tunnel from under their craft and along the sh.o.r.eline towards the city.

Progress was painfully slow at first. Weaker sections under the shifting sands first had to be braced with material scavenged from the interior of the battlecraft, then constantly pumped to prevent flooding. Once a meteor strike caused a collapse that killed six men. But the survivors simply repaired the damaged section and continued. Keldo never let them forget that they were Taklarians: a superior race, the products of a thousand years of selective breeding. To triumph in circ.u.mstances where lesser races might succ.u.mb was their birthright.

He led by example and inspiration, taking his own turn at the backbreaking and dangerous work at the rock-face. If his men had honoured him before, they revered him now, and would follow him into h.e.l.l itself if he ordered it. Keldo was counting on that absolute and unquestioning loyalty to sustain them during the final a.s.sault.

And so the tunnel progressed, metre by painful metre.

They finally reached the city foundations with forty days to spare.

Now fortune smiled on them. Almost immediately they broke into one of the city's main drainage tunnels. It was an ideal location for their secret bridgehead, essential for the next phase of the operation.

Only in the city did the Taklarians' superior natures put them at a disadvantage. Their size and distinctive physiognomies made it impossible for them to pa.s.s among the Arkavians. But they needed to move freely, not only to know the moment the evacuation order was given, but to infiltrate the boarding process of the Ship at the crucial time.

Mechanical surveillance methods were inadequate and potentially disastrous should they he detected. They needed living agents who would not realise they were being used to serve their city's old enemy. Thorken's mind-control technique was the key.

The woman's unexpected discovery of their tunnel mouth.

Keldo now saw, was fortuitous. The test had allowed Thorken to prove that the process worked. The woman had been secretly observed while recovering and showed no indication that she recalled what had been done to her. Tonight they would make their first foray out of the tunnels on to the surface, to reconnoitre and begin the search for more like her.

They would take single subjects and return them, fully conditioned, in under two hours so they would not be missed.

Keldo wanted twenty agents, at least, in place before launch day.

The door tone rang. Keldo came out of his reverie and straightened up. He never allowed the crew to see him as anything less than completely alert at all times.

'Come in,' he said.

An engineer entered, his face grave.

'I regret to report, Sire, that the storm has caused damage to the section of drainage tunnel our shaft connects with. I have had to seal the hatchway to prevent the entire shaft from flooding.'

'How can mere water cause such damage?' Keldo demanded angrily. 'Is that not what the system is designed for?'

'It seems some of the other tunnels have also collapsed, Sire. The flood surges carried a lot of debris. That's what caused the damage.'

Keldo's anger abated slightly and his brow creased in thought. 'That suggests inefficiency. Perhaps the Arkavians are no longer maintaining their drainage system as they should. How long to repair the damage to our tunnel?'

'Many days, Sire. And of course our work may be delayed by the Arkavians' own repairs.'

Keldo brooded for a minute, then said: 'If they are letting their city decay, perhaps they are no longer as watchful as they might be. What is the ground like above the head of our tunnel?

'Loose rock and compacted soil, Sire.'

'Then bypa.s.s the tunnel mouth and raise a smaller shaft to one metre below the surface. We may be able to move more boldly than I had planned.'

'It shall be as you command.'

A thought struck Keldo. 'Do you know if our Arkavian female agent got out of the tunnels before the flood?'

'No, Sire.'

Keldo waved his hand dismissively. 'Never mind. We shall find others.'

Chapter Eighteen.

The Ship 'You do look terribly tired,' Susan said to Ian, her dark eyes full of concern as she sat propped up in her hospital bed.

'Chesterton has been up most of the night looking for Barbara,' said the Doctor, 'but I persuaded him he needed a break.'

'I'm sure you'll find her,' Susan continued encouragingly.

'After all, you know she's already survived a collapsing building. But I'll understand if you want to get back to the search.'

Ian conjured up a rea.s.suring smile for Susan's benefit.

'Actually there's not much more we can do for the moment.

Until the water level drops we can't check the main tunnels properly. Meanwhile, Curton's opening up the most likely access points. There's a chance Barbara reached one of those.

If she climbed the ladder into one of the manhole shafts she should be safe... if she can hold on for long enough.'

'She will,' said Susan, placing her small cool hand over his for a moment. 'She's very determined.'

'I'm certain she will have reasoned the same way,' the Doctor said. 'She must have become familiar with the details of the system while she has been down there. It would be the obvious course of action.'

'Yes, of course,' Ian said, privately feeling less confident than he sounded. Had Barbara's luck finally run out?

'And now we must be going, my dear,' the Doctor said to Susan. You must get some rest and we have things to do.

Since I am giving the Arkavians technical advice, I have requested a tour of their Ship. I want to see this remarkable machine for myself to understand it better.' He glanced at Ian.

'I'm sorry my task is more enjoyable than your own, Chesterton.'

Ian shrugged. 'While you're helping them, I know they'll do their best for Barbara. And it means you'll have the facilities to make a duplicate TARDIS key.'

'I'm sorry I lost my key, Grandfather,' said Susan. 'I must have dropped it when the tower collapsed.'

The Doctor smiled. 'I think it's excusable in the circ.u.mstances, my dear. Never mind. I have ample time to make another one. Meanwhile you concentrate on getting well.

However advanced the treatment you have received, there is no subst.i.tute for proper rest.'

'I have been resting... though I did have a strange dream. I thought I was lost somewhere cold... dark and damp. It was very odd.'

'Well, try to think of something more cheerful,' the Doctor said dismissively. 'At least the mayor a.s.sures me you will not be getting any more visits from over-zealous priests.'

Fostel sat in the private study of his palace gazing morosely out of the window. Through it he could see both the cathedral and the Ship.

And the simple fact was that the Ship overshadowed the cathedral. To be brutally honest it dwarfed it. The Ship might be necessary but it was not right that it was so vast and, yes, he had to admit it, so magnificent and overwhelming. But what was worse, the Church could not take the credit for it.

Functionaries and Technicians had been responsible and as a result they had gained hugely in prestige.

This had forced a bitter about-turn upon the Church. After years of denying Professor Jarrasen the funds he needed for his foolish rocket research, through the council, it had been humiliatingly obliged to turn to him for its very salvation.

Jarrasen had become something of a hero among the people, which in turn increased the standing of his cla.s.s, boosting its self-confidence. Now this self-confidence had evidently grown to such proportions that the mayor felt strong enough to openly defy Fostel himself.

The people were beginning to think that cold calculations and impersonal metal were going to save them, not prayer.

The proportion of committed Believers was falling alarmingly.