Analysing computer data was a laborious task that tended to give Sarah a headache. Perhaps it was simply a game for younger eyes, though hers were surely not old. She considered that for a moment then amended the thought.

Julie Palmer was sitting amidst an array of PCs and monitors, casting her young eyes over the reams of data that were scrolling past. Tsang, Barry and Tom sat around her, sipping coffee, hi Tom's case, sipping coffee laced with whisky.

'So far there's nothing that gives us a clue to where the aliens are.' She frowned. 'Hang on 'Hang on'

A photo of Major Barry was on-screen. Biographical data was scrolling past it. Barry leant forward, mouth agape in a most unmilitary fashion. 'What the hell?'

'It goes all the way back to your childhood, sir. This isn't even a copy of a UNIT record, it's an all-new file.'

'If they know about me, who else do they know about? Can you search for other files like this one?'

'Easily.'

This time the TARDIS materialised inside the plantation house. The Doctor found Chiu supervising the loading of metal blocks into one of two ships.

'Ready to leave?' he asked.

'Almost. There is not enough room for everything, so we will place charges to demolecularise the remaining technology at this site. The house and its environment will not be harmed.'

Good.'

'I am leaving immediately. We will pick up a few remaining crew members in Hong Kong, then proceed to the crash site.'

'I'll join you there soon.' The Doctor hesitated, not unlike Columbo before a 'one more thing'. 'What did you do with the UNIT team who penetrated the area?'

Palmer's fingers were typing furiously but her expression suggested they were doing so independently of her brain. She looked quite disturbed.

'There are new files on Gibson, myself, Captain Clark& Everyone on the field team.'

'Only the field team?' Sarah asked. She thought she could see where this was leading.

'Yes, there's no mention of yourself or Colonel Tsang Colonel Tsang'

Sarah nodded slowly. 'Then they must have known only you. They must have made some kind of contact with you.'

'Tranh,' Barry said slowly. 'He was selling us out, reporting our positions&'

Sarah shook her head. 'No. He couldn't have told them all this stuff about your pasts, could he?' She didn't wait for an answer. She had seen species before who could read people's minds, or extract data from the brain by mechanical or chemical means. It was obvious that this was what had happened to Barry and his group. 'They can only have got this data from you. That means they must have made you forget that they got it, and replaced the memory with the memory of an empty house.'

'Oh shit,' Barry said. He slumped into a chair. Sarah suspected that when this - the ultimate existentialist's nightmare - hit him, he'd be hiding under a table.

'Roger that,' Tsang agreed.

As Chiu described it, they had immobilised the Blackhawk before it could dust off from delivering its human cargo. Had the team been deposited back at the camp without the chopper pilots believing they had flown them, the deception would be uncovered quickly. A disruptor crossfire had pacified the humans before they ever reached the house.

"They were stunned as they approached. We added their pool of knowledge to our own, and then erased the incident from their minds. They returned to base safely, believing they found nothing here.'

"That's very magnanimous of you.'

'Simple practicality, Doctor. If we eliminated them their superiors would know there was a threat here. This way the threat assessment will at least be delayed.'

'Humans may be short-sighted and vicious at times,' the Doctor pointed out, 'but they have some of the most brilliant minds in the universe. They will eventually work out that the team's memory is false.'

'Yes,' Chiu admitted. 'However, operations here are complete. The delay will allow us to decommission this location, and withdraw from it before the Cortez Project can act.'

'I hope so -' The Doctor frowned. 'Before who can act?'

Barry followed Tsang when she left the computer room. The idea that other people could rewrite his memory was just too horrifying to think about. How could he trust his knowledge of anything? People's personalities developed out of experience and memory, so what if he wasn't even who he thought he was? The whole thing was starting to give him a migraine.

Tsang went into her office and picked up the phone. 'Get me the Clancy, code white.' She cradled the phone between shoulder and jaw as she waited to be connected. 'As soon as the Blackhawk returned from dropping you off at your LZ, I had the alien transponder recoded, just in case it was needed for another trip.'

'I'm ready to try again,' Barry lied. In truth, he'd rather that he never left his house again. 'If at first you don't succeed, and all that. Where is it now?'

'Aboard USS Clancy: Barry squinted at her. 'What bloody good is that? I can't get to -' 'It's being fitted onto a Tomahawk. Low-yield tac-nuke: two-and-a-half kilotons.' She got an answer on the phone. "This is Chair. Authorisation to fire is granted.'

The sea a few miles outside Cambodian territorial waters was calm that day as the Spruance-class destroyer Clancy aligned herself into the wind.

Alarms rang as a missile-launch tube was opened.

The side of the ship was obscured by a billowing cloud of smoke as a Tomahawk cruise missile punched its way into the sky. Its small wings were deployed soon afterwards and it began to hurtle inland.

Tse Hung had calmed himself down as the uniformed cops led him and the 49s away from the Doctor's cottage, and drove him back to a police launch moored at a jetty in Silver Mine Bay.

As they approached the launch he manoeuvred himself into the lead position so that he would go aboard first. As soon as his uniformed escort was on board he made his move. He headbutted the cop, knocking him over the side, and kicked the throttle lever on to full.

The launch began to struggle against its mooring rope which Tse Hung cut with a switchblade. By the time the other cops got their guns drawn to fire, he was free and clear.

He wasn't stupid enough to think this was the be-all and end-all of his escape. The police would circulate his description and he'd soon be picked up. He just had to make sure he got picked up by authorities who suited him.

The Tomahawk hit the roof of the plantation house neatly, and exploded within. The nuclear charge was small but it was enough to vaporise the building instantaneously. Metal, aliens, drugs and one 40-foot saucer were ripped apart at the atomic level.

Everything for half a mile in every direction died almost instantly.

'Target destroyed,' a UNIT signals corporal reported. Tsang and Barry grinned at each other. They were back in the computer room, still searching for clues to the aliens' whereabouts.

'Destroyed?' Sarah echoed. 'What do you mean?'

'A low-yield tactical nuclear strike on the aliens' base was authorised,'

Tsang told her.

Sarah was horrified. 'Nuked it? Is that what UNIT has come to these days?

Murdering sentient beings just because they come from somewhere a little more foreign than most?!'

'Nonsense, Sarah. You've worked with UNIT-UK; you know that lethal force is a necessary option only used in the last resort.'

'And what do you call a last resort? Being metal? Having reptilian skin, or two hearts? Having pointed ears in a public place?'

Tsang gritted her teeth. 'I mean when there is a clear and present danger to national, international or planetary security. You have to trim the thorn bushes now and again if you want a safe garden.'

'If that's how you see your duty, then UNIT is no longer an "Intelligence Taskforce" - it's a death squad, plain and simple.' Sarah stormed out, slamming the door behind her.

Tom followed her. 'Sarah, they did what they felt was necessary.'

'Necessary in what way? Surely we'd stopped the aliens interfering in the handover - even if that's what they intended to do.'

'Had we? So long as they were in that base and wouldn't allow us to make contact, they were a threat. Why else would they hide themselves? Why else wipe the UNIT team's memories?'

'You're as bad as the others. 'As disappointing too, but she didn't say that aloud.

'No. Believe me, I'm as upset with the destruction as you are. Those aliens clearly had stealth technology way above and beyond anything we have today, and to simply destroy that is dumb dumb.' He did sound genuinely angry, Sarah had to admit. But whether because of the destruction or the loss of the technology, she was less sure.

"Their technology? Is that all you can think about? What about the local people there, or the wildlife, or the fact that an American nuclear bomb has just been dropped very close to the Vietnamese border? Don't those things worry you just a little?'

This time, she saw the mask move into place an instant before he said, 'Of course they do'. This time she saw that he was being economical with, if not the truth, his own feelings.

The Doctor had returned to the Pimms Building, and was surveying the damage inside it. Yue Hwa found him on the floor that his and Tse Hung's offices were on. 'All the king's horses and all the king's men have really got their work cut out for them today,' the Doctor said.

"That's putting it mildly. 'Yue Hwa looked around, saddened, but in a way relieved. The pretence he had been maintaining was a curse on him, but now he didn't have to bother so much. It was all over, whatever happened.

It wasn't the ending he'd have wanted, but at least it was case closed.

'Is there anything you need from here?' the Doctor asked.

'Yes, from my office.' The two men entered the room. There was water damage to the furniture and papers, from the sprinklers, but nothing seemed to have been burned. Yue Hwa moved a small drinks cabinet aside, revealing his office safe set into the wall. From it, he drew a small photo frame.

To his eternal relief, the pictures within were undamaged. They were of a reasonably average woman and a baby. The photos were all he cared about in his office. The rest could burn as far as he was concerned.

'Your wife and son' the Doctor said understanding^.

'Ex-wife by now, I imagine, 'Yue Hwa corrected him. 'I haven't seen either of them for two years.' The Doctor didn't say anything, but Yue Hwa could sense what was probably disapproval. Or maybe he was just imagining it because he disapproved of himself.

Yue Hwa hadn't been there when Lai Ching was informed he wouldn't be coming back, but - from what he'd been told, and what he knew of her -he felt he could picture how the day had gone.

The PSB deptutation would have been made up of two people, a man and a woman. They'd have told her about his abandoned car near the border with Hong Kong. They'd have theorised about how he had probably sneaked across on foot, or stowed away in a truck. How he'd disappeared without trace.

Lai Ching would have cried a little, but not too much. They got on all right but they weren't really that close anymore. It was one of those stay-together-for-the-sake-of-the-child marriages. Add in a healthy dose of not wanting to mortify either family by splitting, and you had a less than heavenly match.

But neither of them abused the other, and there was still love, however stale.

There would have been few tears from Lai Ching, but at least they would have been genuine ones. After a year, perhaps she'd have had him declared legally dead. He certainly didn't see her waiting in the hope that he'd return, especially if she thought he'd simply run away.

If he could have told her anything else, he would have, but the story she was told was the best one he could think of that would have the desired effect. It was the best story keep her out of danger.

If anyone knew he had a wife and child, they could use them against him.

He wouldn't jeopardise his mission that way, and neither could he have put his family in such a position. So he had to run out on them instead. He doubted that anyone would ever believe it was for their own good.

"These things will work themselves out,' the Doctor said, drawing Yue Hwa back to the present and the ruin.

'I wish I could be certain of that,' Yue Hwa whispered. Such things were beyond the knowledge of men.

'You can,' the Doctor assured him.

Inside the computer room, the signalman re-entered, rather more subdued.

'Radar-tracking picked up two signals leaving the target a few minutes before the nuke hit. We may have got their base, but we haven't got all of them.'

Tsang cursed. 'Where were they going?'

"They visited Hong Kong, but one left again. We don't know where they're going. At least, we're not sure.'

'Not sure?'

"There's a man outside who says he worked for the Doctor. He says he knows where the aliens are going, and wants to make a deal.'

Chapter Twenty.

The Cortez Factor

The engines of the Hercules were already running when the pair of Discoveries pulled up nearby at a runway at Chek Lap Kok. Sarah was in the lead car with Tsang, Barry and Tom. Tse Hung, Gibson and Harris were in the second vehicle.

Although the airport wasn't yet officially open, Sarah could see it ought to be a great improvement on Kai Tak when it was ready. She wondered how long UNIT had been using the place for covert flights. 'Can we trust this Tse Hung?' she asked. Frankly, she doubted she could trust anyone associated with the situation she was in.

'We can trust his desire to screw the Doctor over,' Tom said. "The Triads have a certain way of looking at things.'

In response to a ground crewman's direction, Barry slowly guided the Discovery up the tail ramp until locking clamps grasped its wheels inside the cargo bay. They exited the vehicle as the second Discovery followed them in, and headed through to a small passenger section.

'How long a flight will this be?' Tsang asked.

'It's about nine hours to Riyadh,' Barry answered. "Then another couple of hours to get to the coordinates Tse Hung gave us. Their saucers are a lot faster of course; we might not be in time to prevent them doing whatever it is they want to do.'

Tsang grimaced. 'It's a damn shame Tse Hung doesn't know that. Still, I've managed to get the Americans to have a ship take up position over the coordinates he gave us.'

Sarah harrumphed.

This isn't over,' the Doctor told Yue Hwa. They were standing in the remains of the Pimms Building, eyeing the damage. 'Our other conspirators -'