He should have realised it was not the right time to lay down the law. Lant's disrespectful treatment of him had clearly reduced his authority in Plax's eyes. The boy was still young enough to find that hard to accept. His pride was wounded and he had to strike out against something.

'Why shouldn't I?' Plax had retorted indignantly. 'Chasing a few escaped NC2s doesn't do any harm. The Watch are after them anyway.'

'That is their job. It's not seemly to be too closely involved with either them or with escaped criminals. Let's just say I would rather you did not go into the Outer Zone again.'

But Plax would not let the matter rest. 'Why not? We don't bother anybody. The people keep out of our way.'

'Plax, don't argue, just do as I say for once. It's for your own good.'

Plax's mouth set in a stubborn line. 'I think I'm old enough to know what's good for me,' he had said, and stormed out of the house.

It was after breakfast when Orm Herstwell called, wanting to know if Plax had come home yet. When he learnt he had not, he reluctantly admitted the challenge he and his friends had set him.

'We returned to the same spot early this morning,'

Herstwell explained, 'but Plax wasn't there. At first we thought he was getting back at us but, after a while, when he still didn't appear we began to wonder if he'd had some sort of accident. We searched the area pretty thoroughly but there was no sign of him. In fact there was no sign of anybody. The whole area seems deserted. Has something happened out there, sir?'

'Never mind about that,' Vendam said quickly. 'You and your friends are not to leave the Inner Zone again, do you understand me?'

'But what about Plax, sir? We feel responsible. We'd like to help find him.'

'I'll take care of Plax,' Vendam a.s.sured him.

After Herstwell had gone Vendam sat for several minutes staring bleakly into s.p.a.ce. What had happened to Plax? Some of the buildings out there were dangerously fragile. Perhaps he had gone inside one for shelter and a floor had given way.

There were any number of possibilities. And even if he was safe, he could not wander around for long without realising the truth. There could be serious repercussions if the actions of his own son and others of his cla.s.s exposed the deception. Even if the discovery was successfully suppressed the incident would dangerously strengthen the hands of the mayor and the Church, to the detriment of the Elite families.

Therefore he couldn't call the Watch in to help... at least not for a few hours.

But he couldn't leave Plax out there either. When all was said and done, he was still his son and his responsibility.

He picked up the house phone.

'Meeks... have my car made ready... No, I wish to drive myself.'

'You are not Susan, you're an android, a simulacrum, an impostor!' the Doctor said. 'What have you done with my Susan?'

As she had for the past half hour, the thing that looked like Susan Foreman sat huddled in a chair hugging her arms about her, face pale and incredulous, eyes red-rimmed, cheeks tear-streaked. Despite knowing the truth, incredible as it was, all Ian could think was how very frightened she looked.

'Please stop it!' she begged. 'Grandfather, don't say those things. You know who I am!'

Nyra Shardri held up a sheaf of print-outs from her medical scanners. She had recovered from her initial shock and was almost as angry as the Doctor. She had been badly deceived and now one of her patients was missing.

'You look like Susan, and something inside you fools the automatic scanners, all right,' she said. 'But the biopsy probes I made prove what you are: flesh grown over a gellfibre musculature and magnoalloy skeleton, with synthetic internal organs and a block of crystal micro-circuitry for a brain.'

'But when was the switch made?' Ian wondered.

'Susan wasn't like that when she came in here,' Nyra said, 'I saw that with my own eyes. And she was under continuous observation since then... except for the kidnapping.' She glared at the android again. 'Is that when you were subst.i.tuted?'

'I don't know!' the android said desperately.

'Could the bishop be responsible?' the Doctor asked Lant.

'I don't see the Church using technology like this,' Lant said. 'I didn't even know this sort of thing was possible. If it was them, then that ceremony we interrupted was staged and we were meant to get her... this fake... back.' He frowned.

'Then they spoilt everything by wounding her. Was that just an accident, or does it mean they didn't know what she was either?' He rubbed his eyes. 'Sorry. It's been a long night and this is getting beyond me.'

'It must know the truth,' the Doctor said, glaring balefully at the android. 'And it will tell us.'

'Doctor!' Ian said sharply. 'I know you're afraid for Susan... the real Susan, but you're frightening it... her. I don't think she knows. Maybe as far as she's concerned she is Susan. If she's a machine, couldn't she have been programmed to believe it, or something? Well?'

With a visible effort the Doctor restrained himself and instead sat down heavily, resting his head in his hands. He suddenly looked very old.

In the weary silence the android Susan appeared to take in a deep breath and steady herself. She looked at the Doctor with sad longing, then reached out for the print-outs Nyra was still holding so accusingly.

'Please,' she said.

Nyra handed them over with grimace of distaste. The android examined them carefully. After a minute Ian saw her shudder but keep reading. When she was finished she closed her eyes tightly and Ian wondered if she was crying. Could a machine really cry?

Without warning she sprang to her feet, spun round and punched the wall behind her with all her strength, crying out not in pain but from inner anguish. They looked on in shocked silence. Slowly she withdrew her fist from the indentation it had made in the wall panel and looked at her bleeding knuckles expressionlessly. Then she turned to the ring of grim faces surrounding her, her gaze finally settling upon Ian.

'I remember being on Earth in 1963. I was a pupil at Coal Hill School and I gave you such problems in science cla.s.ses...

Then you and Barbara followed me back to Totter's yard.

That's right, isn't it?'

Ian nodded. The android looked at the Doctor, who reluctantly met her eyes.

'You were so angry with them for prying, Grandfather...'

she faltered '...Doctor. In fact you were quite rude. I recall every detail. But if I search deep enough I don't think those things happened to me... but I can only tell because I know the truth about what I am. It takes an effort to look that hard. If I stop... then I am Susan and this is a nightmare.'

The Doctor said: 'Why were you given Susan's memories?

Who was responsible?'

'I don't know,' the android said wretchedly. 'I really don't know!'

Ian stepped forward and took her hand. It felt perfectly normal. 'I believe you,' he said. He looked round at the others.

'Let's stop blaming her for something she can't do anything about.'

'All right,' said Lant. 'But what am I going to tell the mayor? I've already said we'd recovered Susan safely. Now how do I explain this?'

Archdeacon Zeckler looked down on Fostel's body as it lay in a closed side-chapel in the cathedral.

It had been moved with indecent haste from the health club, before a larger force of watchmen descended upon them.

Now, standing among the solemn candles and sweet smell of incense, Zeckler realised the burden of guardianship had pa.s.sed to him. He gave a silent prayer up to the Maker that he might make the right decisions. Only a handful of the brethren knew what had happened for the moment, but in a few hours he would have to make some sort of public announcement. He must decide how to reveal the circ.u.mstances to the greatest benefit of the Church.

Of course, the bishop's demise had, technically, been accidental. He had fallen into the pool in the darkness and confusion and, with tragic irony, had been dragged to the bottom by the weight of his own robes. But Zeckler knew that in the Maker's eyes the watchmen and the aliens, and even the mayor, were responsible, though it would be difficult to prove this to the unenlightened citizens. It was almost regrettable that the late bishop did not bear the mark of violence. A bullet wound from a watchman's gun, now that could have been turned to good purpose.

Zeckler hesitated. Was this divine inspiration?

It was not too late to add such a detail to the remains to reinforce the greater fundamental truth. He was sure Fostel would understand. After all, what was left of him was now only an empty sh.e.l.l of flesh and blood.

Chapter Twenty-Six.

Tidal Stress From the day of the asteroid impact, fissures had been extending through the core of the falling moon.

Every time its irregular ma.s.s pa.s.sed close to Sarath the tidal force acting across its one hundred and fifty kilometre width opened the cracks a little further, as the opposite sides of the moon tried to orbit at slightly different velocities. In addition to the gravitational stress, there was the interaction between Sarath's magnetic field and the ferrous lodes within the moon's core. Even as this force slowed the moon's forward motion, the lodes twisted and flexed against the rock around them. Myriad cracks met and merged and sheer planes formed. Deep within the moon, rock grated against rock through fractured strata whose combined surface area would have measured many tens of kilometres square. Inexorably friction generated heat.

As the moon spiralled ever closer to Sarath the stress force at its heart multiplied. Unable to radiate away into s.p.a.ce, the gathering pool of heat around the fracture zones began to melt the surrounding rock.

Magma chambers formed and sent questing roots back up through fissures towards the surface. Steadily the pressure of the molten rock rose until it could no longer be contained.

Chapter Twenty-Seven.

Rift 'You shouldn't have allowed Lam to play the hero,'

Commander Pardek told Draad angrily.

'I was trying to avoid taking any official action against Fostel,' Draad snapped. 'You know I couldn't move without proof. We never expected that the bishop's men would be armed.'

Both men were tired and short-tempered. They had little enough sleep at the best of times and this last night had been worse than usual.

'Yes, and if we'd had a proper team in there we could have had him for holding illegal weapons,' Pardek replied with barely concealed disgust. 'As it is, by the time my squad got there the place had been cleaned out of anything incriminating. The weapons are probably stored all over the city by now. We know one of their cars delivered something to the cathedral, but they got it inside before we could intercept them. Do we risk making a search?'

Draad shook his head. 'The Watch has never set foot in the cathedral on official business since it was consecrated, far less searched it. I want to keep the Believers off-balance, not provoke an all-out confrontation.'

'But we can't let them keep unlicensed weapons.'

'We may have to. At least we know they exist now.'

'Your pardon, Mayor,' Monitor interrupted, 'but standing orders require that I inform you immediately about any changes in the condition of the moon. Observations from our remaining automatic equatorial stations show rapid changes on its surface.'

'Let's see them,' Draad said.

Wall screens lit up to show the scarred body of the moon seen from three different camera positions. One view was intermittently obscured by wisps of drifting cloud, but the others were clear enough. They showed a cl.u.s.ter of half a dozen flickering red points of light on the moon's limb. Even as Pardek and Draad studied them they grew more intense and new spots sprang up about them. In minutes they were forming into crooked lines that radiated outwards across the moon's surface.

'Volcanoes?'

'Apparently so, Mayor,' Monitor confirmed.

'But where did they come from... and why are they appearing now?'

'Internal heat may have been generated by c.u.mulative stresses within the moon's interior. They are erupting along pre-existing fault lines, which would provide points of least resistance to subterranean magma pressure.'

The flickering volcanic vents were being obscured by dark clouds of ejected material. About them the normally sharp surface features were being blurred as though by a rolling fog.

In its last days the moon was gaining a temporary atmosphere of dust and vaporised rock. Occasionally it was lit from below by ruddy glows and blue-white electrostatic discharges.

'Will these eruptions affect our projections for Zero Day?

'Pardek asked anxiously.

'Not at their present magnitude, Commander,' Monitor said. 'Any net thrust the volcanoes impart to the moon will not alter its trajectory to an appreciable extent in the time remaining. Ejected material that reaches us will add negligibly to the residue from the primary event still impacting Sarath.

The Ship's intended escape trajectory should carry it clear of any fresh matter in orbit.'

'Good,' Draad said. 'Continue close observation just in case.

'As you request, Mayor.'

Draad and Pardek resumed their deliberations. They were wondering if Fostel could be reasoned with privately when Monitor interrupted once again.

'Mayor. An unscheduled live broadcast is being made from the cathedral.'

'What? Put it on.'

Archdeacon Zeckler's grave features filled the screen.

'Fellow Believers, citizens of Arkhaven,' he said. 'It is my sad duty to inform you that Bishop Fostel is dead. He was tragically killed during the early hours of this morning while conducting a special ceremony in the private premises of some of his closest followers.'