'I see,' said the Doctor. 'Well, thank you for trying.

Captain.'

'I haven't given up yet. I'm still waiting to hear about the ongoing search. The trouble is I was only a.s.signed to this squad temporarily, so I don't know how to get the best out of them yet.'

He moved aside again, putting the phone to his ear.

Another matter had been troubling Ian. 'What was it about Susan's medical report that has them so puzzled? If they're originally from Earth, why should we seem different to them?'

The Doctor gave him a peculiarly penetrating look, then sighed. 'Evidently you have not yet fully grasped the facts about our antecedence, Chesterton. A pardonable mistake in the circ.u.mstances, perhaps. You see, Susan and I are not actually...'

Mayor Draad opened the door of his office: 'Please come back in again, gentlemen.'

One of the screens on the office wall now displayed the image of a tired-looking middle-aged man whom Draad introduced as Professor Tovel Jarrasen. The professor stared back at them with sceptical curiosity. Draad gestured out of the rain-streaked window at his back towards the towering bulk of the Ship.

'You know what that is, I take it?' he asked Ian and the Doctor.

'We've picked up the basic facts,' Ian replied. 'Your moon is falling.'

'Yes. By our best estimates it will strike in thirty-three days' time. Monitor: display a current image of the moon.'

'The moon is about to rise over station seven,' a measured voice said.

Another screen lit up to show the night sky over a jagged horizon bathed in a pearly glow that grew stronger by the moment. Suddenly the horns of a crescent moon appeared, rising at incredible speed. Of course, Ian thought, it's moving against the rotation of the planet. In moments a rugged crater-scarred body fully fifty times wider than the full moon of Earth was soaring into the sky.

The camera tracked its progress. Before it had reached a quarter of the way up to the zenith the moon began to redden and dim, then faded into a black silhouette eclipsing the stars.

'It has now pa.s.sed into Sarath's shadow,' the voice of Monitor said.

'That was relayed from an automatic station on the equator,' Draad explained. 'The moon's so close now that it's no longer visible from these lat.i.tudes. Perhaps the fact that the people can't see it any more helps to maintain a sense of normality.'

'It orbits in your equatorial plane?' the Doctor asked.

Unexpectedly Monitor answered: 'The deviation is no more than eleven degrees, Doctor.'

The Doctor blinked. 'Your computer seems to know who we are already,' he observed.

'Monitor is a very sophisticated machine, Doctor,' Draad explained. 'We could not run Arkhaven without him. A duplicate of his mainframe unit has been installed in the Ship.

He will be coming with us to aid our colonisation of Mirath.'

'I see.' The Doctor looked into Monitor's camera eye.

'What do you think of such an undertaking, Monitor?'

'I am programmed to serve the city, people and lawful rulers of Arkhaven. If the city state of Arkhaven is transferred to Mirath I will continue to serve it there with the same efficiency.'

The Doctor nodded. 'I see. Well, it is a most remarkable project you are undertaking, Mayor.'

'We have no choice,' Draad said simply, 'considering the alternative...' He faltered as though he could not bring himself to speak further and gestured at Monitor's camera eye. Tell them the projections.'

'When the moon strikes it is estimated it will penetrate to a depth of forty kilometres,' Monitor explained. 'The shock wave transmitted through the mantle will open up geological faults across Sarath, releasing lava flows that will cover 65 per cent of the surface. The impact will throw superheated dust and rock of gigatonne magnitudes into the stratosphere, obliterating the sun. When these fall back they will incinerate all remaining organic matter. Life in the oceans, if any still remains, will die as the plankton at the base of the food chain is poisoned. The oxygen will be burnt out of the air by the planet-wide fires and will not be replaced, since insufficient light will reach the surface through the dust-polluted atmosphere to initiate photosynthesis. Sarath will be a sterile world experiencing major earthquakes and volcanic eruptions for an estimated minimum of eight hundred years.'

Ian was silent. Monitor's emotionless catalogue of disaster was chilling. He could think of no suitable response after such an apocalyptic p.r.o.nouncement. The Doctor was less inhibited.

'You have our sympathy,' he told Draad gravely. 'But I'm afraid we cannot offer any solution to your problem. Even if I had access to the TARDIS I could not carry you all to safety.

Nor do I have the means to deflect or destroy your moon before it strikes.'

'I was not expecting miracles,' said Draad. 'But nevertheless you can help us. I have a proposition. We will give you the facilities to make another key for your machine if, in return, you give us your knowledge.'

'Knowledge of what?'

Professor Jarrasen spoke up.

'I am the princ.i.p.al designer of the Ship, Doctor. If your own craft is all that you say then perhaps ours seems very primitive to you. But I a.s.sume, as s.p.a.ce travellers, that you have at least studied similar devices.'

The Doctor swelled slightly. 'I have a sound working knowledge of atomic rocket technology,' he admitted.

'The Ship is untried and largely untested. The war interfered with much of our research programme. Our practical experience of s.p.a.ce travel is limited to the launch of a few unmanned research probes. The normal development process has simply not been possible; consequently there are many details that could be improved. If you could check them over we still have time to make any minor modifications you could suggest.' Jarrasen forced a wan, tired smile. 'You see, I'm not too proud to ask for help. All that matters is that the Ship works and carries us to Mirath safely.'

'Well, Doctor?' Draad asked. 'I think we have a right to seek any help we can get. For the sake of humanity, will you help us?'

'Is it humane that you're going to leave the NC2s behind when you go?' Ian asked accusingly.

Draad pinched the bridge of his nose and his shoulders seemed to sag for a moment. 'Don't you think I would save everybody in Arkhaven, native or not, if I could, Mr.

Chesterton? But the pa.s.senger capacity of the Ship, plus essential supplies and equipment, was established before the last influx of refugees. We are working up to its safety margin as it is. Don't you agree that it is better to save some than risk losing all in an overloaded vessel?'

'But you are deciding who lives and dies by accident of birth. Natives of Arkhaven get preference over everybody else.'

'And why not?' Draad responded with a little more vigour.

'We conceived the plan and poured time and resources into the project. We persevered even through the war with the Taklarians. Why shouldn't we be the first to reap its benefit?

There is only one vessel in the world capable of reaching Mirath and it has fallen to me to choose who will ride in it.

Believe me, I didn't ask for such responsibility, but I will stand by my decision.'

Ian said no more. He simply nodded in mute understanding.

'So, Doctor,' Draad asked, 'will you help us?'

The Doctor looked thoughtful. 'Before I answer, there is one question I would like answered.'

'What's that?'

'Why are you illuminating empty buildings and putting dummy drivers into robotically driven cars?'

Consternation showed on the faces of all three Arkavians, but the Doctor glared back at them stubbornly.

'Come now,' the Doctor continued. 'You cannot expect our cooperation while keeping such a thing secret. Just what are you hiding and why?'

After an uncomfortable pause Draad nodded. 'All right,'

he said to his compatriots, 'I'll take the responsibility... and answer to the council if necessary.' He turned back to Ian and the Doctor. 'What I am about to tell you is only known to essential military and government personnel. I must ask you to respect our confidence and to divulge this information to no one outside this office.'

'We can promise nothing until we know the facts, sir,' the Doctor said stoutly. 'Only you can judge whether this revelation is worthy of our discretion.'

Draad sighed. 'Very well. I just hope you will understand.

It all began during the war. Spy drones determined the nature of the Ship once full-scale construction began and the Taklarians threatened to destroy Arkhaven unless we agreed to take them with us. But apart from such an option being morally repugnant, we knew the Ship could not carry them as well. Their battlecraft still held several thousand warriors. So they began their attacks. To avoid damaging the Ship they concentrated on the outer suburbs. To maintain public morale we did not dare to divulge the true numbers of casualties. The city council formulated the policy of diverting all available resources to repairing superficial damage as soon as possible.

'Even when there had been considerable loss of life, we tried to make the damaged areas appear populated. Firstly we used soldiers, then simple automatons and automatically controlled vehicles. This also had the effect of deceiving the Taklarian drones, misleading them as to the effectiveness of their attacks. Ruined buildings were patched up and illuminated at night to make them seem occupied, public information screens were kept running, and so on.'

'Wasn't there a blackout?' Ian asked.

Draad looked at him curiously. 'City lights made no difference to the accuracy of the Taklarian weapons. They did not rely on simple optical target-seeking.'

'And a brightly illuminated city was also better for morale,' the Doctor suggested.

'Exactly,' Draad said. 'Anyway, as losses mounted and s.p.a.ce became available, the surviving citizens steadily moved inwards from the outlying districts towards the heart of the city. It was, and still is, the safest place to live. People keep to the Inner Zone just to be near the Ship. It's a powerful symbol.

'Luckily Arkhaven is in a relatively stable geological area, so we've had little seismic damage. It's also self-contained.

We can fabricate material goods, synthesise food and have ample reserves of power.' Draad hesitated. 'We've heard nothing from outside for half a year. As far as we know, Arkhaven is the last outpost of civilisation on Sarath.'

'But the war's over now,' Ian said. 'Why continue this deception?'

'To make the citizens feel safe,' Draad said bluntly. 'They know there are some deserted areas in the Outer Zone, of course, but not their true extent. They see occasional news reports from outlying districts with automatons in the background to swell the numbers. They are insulated from a desolate world by that band of brightly lit towers. They don't think to wonder whether they are really occupied. Individuals know of family or friends lost, naturally, but only a few of us know the true total.'

'How many did you lose?' Ian asked.

Draad hesitated, apparently too pained to speak. Monitor answered for him.

'Arkhaven had a population of five million one hundred and two thousand before the war, Mr Chesterton,' it said.

'Now there are slightly under eighty thousand registered citizens left.'

Ian felt numb. 'You lost over five million people!'

'We had taken rising casualties for almost four years of war in addition to storm losses,' Lant said. 'Then, near the end, the Taklarians used a new form of chemical weapon on the Outer Zone... it worked only too well.'

'But you can't conceal such a huge loss of life,' Ian persisted. 'People would notice even with your cover-up.'

'Would they, Mr Chesterton?' Draad asked with a humourless smile. 'Tell me, do you live in a city in your world?'

'Yes, London... our capital.'

'What is its population?'

'Well, there are almost eight million in greater London the centre of the city.'

'Really. Have you counted them personally?'

'Of course not. But there are census statistics...'

'And the census is government controlled?'

'Of course...' Ian faltered for a moment. 'All right, I see what you mean. But I can tell there are tens of thousands of people living and working around me every time I take a walk or travel to work. From that I can estimate the total population of the city.'

'Do you travel down every road to see it is equally busy, or examine every person you pa.s.s to know they are real?'

Draad asked. 'Do you not actually see most people at a distance or enclosed within vehicles, or simply infer their presence from lights in buildings?'

Ian hesitated.

'I believe the mayor has made his point, Chesterton,' said the Doctor, smiling grimly.

'The people will learn the truth when they reach Mirath,'

Draad said. 'But by then it won't matter. We'll have done what was necessary.'

The Doctor glanced at Ian, who nodded.

'Your secret is safe with us,' the Doctor a.s.sured Draad.

'Meanwhile, I will be pleased to look over your designs and make any suggestions that seem appropriate.'

On the screen Jarrasen smiled in relief. 'Thank you, Doctor. I'll sort out the details of the areas I'd like your opinion on.'

His image vanished.

'I'd like to go back to the building where we landed,' Ian said. 'To see if there's any news of Barbara.'

'Of course,' said Draad. 'I'll a.s.sign Captain Lant as your liaison. He'll take you anywhere you wish. Would you like to visit your granddaughter, Doctor?'

'Thank you, sir,' the Doctor said. 'I was hoping to see her before I start work.'

'I think we can spare you a few hours, gentlemen. Our time may be precious, but we strive to maintain a sense of order and civility. It will be all that sustains us through the last days of the world.'