'Are leaving Hong Kong. They're no longer my problem. 'Yue Hwa didn't meet the Doctor's eye and the Doctor jerked round, trying to catch his gaze.

"They're everyone's problem, whether the rest of the population of this planet knows it or not. They still need help to get their ship repowered.

They need our help. You can't just abandon them.'

Their eyes locked. 'I couldn't, if it was up to me. But I have new orders from Beijing. When the People's Government takes over Hong Kong they'd like to have an immediate reduction in the organised crime problem. They don't want their new capital of capitalism to go the way of Moscow.'

'If we don't finish what we started, their capital of capitalism, and all their other cities, will end up going the way of Hiroshima or Pompeu, let alone Moscow.'

'I've tried to tell them that.'

"Then tell them they're fools!' The Doctor tossed his hat to the floor. He looked at it with a regretful expression. 'Anger. Always ends up damaging only what you care about.' He lifted the hat with the tip of his umbrella and put it back on. He sighed and turned back to Yue Hwa, his mood seeming to flip over completely. 'I think we just need to tell Beijing what they need to hear.'

'And that would be ?'

'If we don't fulfil our obligations to our extraterrestrial friends, the Americans will probably get to them first, and grab both them and their technology. Now, will Beijing really want the Americans to have access to all manner of wonderful alien weapons, which are centuries in advance of anything anyone on Earth has now?'

When Yue Hwa put down the phone after passing the Doctor's question along to his superiors, his ear was almost burning. 'Well?' the Doctor asked eagerly.

"They want to know why I'm not already at Kharg Island. I'm editing that sentence, of course. There were a lot of rude words in it.' He sighed. 'All right, how do we get there?'

The Doctor looked at his thumb. 'We hitch a lift.'

Just as Sarah had been in years past, Yue Hwa was impressed by the way the Doctor made such miracles seem so casual. Over the past few months, he had become accustomed to the truth of alien life, but he had a long way to go before it could ever become a casual thing.

Sarah would have told him that it never became a casual thing; not really. A lot of people who had met the Doctor or other aliens acted as if they took a casual view, but they were fooling no one, least of all themselves.

The flying saucer's transparent floor made the trip dizzying as the blurred desert zoomed underfoot.

'How long?'Yue Hwa asked. He lifted his eyes to the ceiling. There was no sense of motion in the circular flight deck, and the view of a plain metal roof was a lot easier on the stomach.

'Perhaps five minutes,' Chiu replied.! assure you that I am as keen as you to complete this journey. Though I have further to go go'

'It isn't easy being separated from those at home, 'Yue Hwa said understandingly.

For a moment it seemed that Chiu was going to say something touching, but then he merely nodded.

'Being a stranger in a strange land isn't the easiest subject to talk about,'

the Doctor said softly to Yue Hwa. 'He understands that just as much as you and I do.'

Yue Hwa stepped back and lowered his voice. 'Does Chiu have a family at home? Someone to miss, or to be missed by?'

'Not in the way you mean,' Chiu said clearly, before the Doctor could answer. 'But there are those who would would care, if that is the right word.' care, if that is the right word.'

The land around Prince Sultan AFB on the outskirts of Riyadh is flat and largely featureless. If it weren't for the occasional distant building, you'd almost think it was an outpost on some lifeless uninhabited planet.

The impression is misleading, of course; the desert teems with life, and Riyadh is the capital of one of the richest states on Earth.

Major Barry felt a lot more comfortable here than he had in the jungle. It was hotter in the desert, but not as stultifyingly humid. He didn't feel quite as filthy as he had in Cambodia and, as far as he was concerned, that was enough to make the place worth visiting.

Tsang - who was in the passenger seat of the jeep he had borrowed -had arranged billets, food and showers at the base, but had forbidden any discussion of operations, even among themselves. One of UNIT'S EC-130 airborne HQs was already on site in a distant corner of the dispersal field, and that was the only place where any of them felt safe to talk.

The Smith woman was approaching the Hercules as Barry pulled up in the jeep. 'Need a lift? The fun chat can't start till we get there anyway'

'Thanks,' Sarah answered, with great relief. "It's a longer walk than I thought.' She got aboard and Barry cruised over to the plane and parked a few yards from the tail ramp. 'What are we going to be discussing?' she asked.

Barry smiled apologetically, regretting that he had to draw his pistol on Sarah. "The Cortez Project.'

A small office was set into the front of the Hercules, just behind the cockpit. 'Wait outside,' Tsang told Barry. He closed the door, and Sarah felt she was being locked in with a tigress. Or a black widow.

A tray of refreshments had been left on the desk for them and Tsang began helping herself to an iced tea. Sarah stuck with the more trustworthy option of the coffee-pot and a couple of sugars.

'Do you know your history?' Tsang asked.

'I did an A level,' Sarah answered. 'I don't know if that quite qualifies.'

Tsang sipped at her iced tea. 'When Cortez landed in South America in the sixteenth century, he burnt his ships, so that his men would have to integrate with their new environment or die.

'In human history, every time two cultures or societies at unequal stages of technical advancement have met, it has led to the demise of the less advanced culture, the prime example being when the Europeans began exploiting the New World.'

'Starting with Cortez'

'Correct.' Tsang smiled. 'By definition, any alien race that comes to this planet must be more advanced than us. That makes them a clear and present danger to human society itself'

'You can't be saying that every race in the universe wants to conquer the Earth! Surely there are a lot of visitors who have rules about non-interference -'

'Oh, spare me the Star Trek crap! I'm talking about the real world; the real galaxy. I've been in UNIT a long time, and just about every set of extraterrestrials I've so much as read a file on has turned out be hostile.

The few - the very few - who weren't actively hostile have turned out to be naturally inimical to human life, and so would be a threat even without intending it. When Cortez brought Europeans to the New World en masse they didn't just conquer and plunder, of course; they brought a new religion and all the laws that were based on it. They brought syphilis and plague& Even following the dictum of "make love, not war" still brought about massive damage. Think how much more damage an alien incursion may cause.

'Say they bring a cure for cancer or the aging gene - then maybe we'd become sterile as a result. Or run out of food and water.'

'So you think it's safer just to kill them.' Sarah was repelled. Prejudging a potential event was bad enough, but to use it as an excuse for murder murder 'That's right. Safer for all of us.' Tsang leant forward imploringly.

'We must not allow any of these civilisations to endanger our own existence. If we can hide from them, fine. But if they come here, it's them or us.'

Sarah felt a desperate need for fresh air, but there was the guard outside& She could always try to throttle Tsang for her insane views, but doubted she'd get very far in that line. It wasn't just the nature of Tsang's lecture that had disturbed her. She knew it must mean she was in danger. Tsang would never have told her all this stuff if she was just going to let Sarah walk right out of here. 'And the Cortez Project is the scheme to prevent this this disaster?' disaster?'

Tsang nodded, apparently pleased. 'The Cortez Project is a group of people who understand the threat we face, and are willing to do what's necessary to deal with it. UNIT, as you know, was formed to deal with "new and unusual threats" to mankind. Most people, even within UNIT, think that should refer only to outright hostile visitors. Those of us who know our history can see that this isn't the case; that any contact is a threat. The Cortez Factor, if you like.'

'Then this isn't UNIT policy?' That was a relief.

'Unfortunately, not yet. The Cortez Project runs within UNIT, without the knowledge of the secretary-general or the defence ministries of any of the member countries. We'd like you, as an attached member of UNIT-UK, to join us.'

'Why me?' Sarah managed to make it sound like a calm and reasonable question, which wasn't how she felt.

'In your time with UNIT-UK and with the Doctor you've seen for yourself how much of a threat this planet faces. Your file makes it clear you've been involved in several events in which the destruction of humanity itself was a direct possibility.'

'And if I refuse this offer, I wake up next to a horse's head?' Tsang merely looked baffled at that. 'I mean, you'd hardly let me walk out of here, knowing all this, if I refuse.'

Tsang didn't stoop to confirming the threat. Neither woman needed to be so obvious. She didn't deny the assumption either. 'You're ideal,' Tsang said quietly. 'You're experienced, you have contacts and you know the dangers - even from your former friend, the Doctor. Look at him now: a gangster collaborating with alien infiltrators. If that doesn't prove the Cortez Factor, I don't what does.'

Chiu's ship had come to rest on a concrete dockside that jutted out into an almost unnaturally blue sea. At first Yue Hwa wondered why the saucer didn't attract further attention, but when he disembarked he found that it wasn't there to be seen. Only a faint haze in the air betrayed its presence.

He and the Doctor helped Chiu and his people carry several crates and boxes out of the ship and across to a black submarine moored at the dock.

'Welcome aboard.' The captain greeted them in a thick Russian accent. He waved to a couple of sailors to help with the cargo.

None of them could believe how cramped the interior of the submarine was. Yue Hwa had once spent a week staying in a Japanese 'capsule hotel', where the room was a cocoon little larger than his body. The living quarters aboard the Zhukov were worse still, like a capsule hotel designed for children, and slept several men in each bunk.

As soon as one man went on duty another took his bunk, through three or four shifts. The beds were always body-warm. Yue Hwa thought he'd go crazy in such a situation. He was a country boy at heart, and found it depressing enough living in an apartment in a crowded city, but this was a living hell.

Even Chiu looked surprised by the lack of room. 'This is an inefficient design,' he noted. 'It will cause friction among the crew, reduce morale and thus impair combat efficiency. You should change it,' he told Captain Kutzov. 'You can find the coordinates again?'

'Easily,' Kutzov boasted proudly. 'My navigator is best in fleet.'

One of the Russians came and said something to the captain. He looked up. 'Well, we're past the point of no return now. Welcome to Iraqi territorial waters.'

'You say that as if it's a bad thing,' Yue Hwa said dryly.

The captain looked at him. 'This will not be easy. The Americans keep a carrier battle group in the area at all times, to help enforce UN no-fly zones.

Where there are American aircraft carriers, there are Aegis cruisers, and more anti-submarine helicopters than there are fleas on dog. Sooner or later they will find us.'

'What? You're trained to hide underwater, surely? Run silent, run deep?'

The captain nodded. 'Sure. But Persian Gulf is coastal waters only. It is never deeper than, oh, one hundred metres. Not deep enough to hide for long.'

Sarah had thought that travelling in the TARDIS was confusing for her body clock, but that form of time travel was nothing like as draining as making several east-west trips over several time zones in a matter of a few days.

Hours ago she had stopped trying to work out what time it was in London, and settled for the determined idea that it was bedtime. Unfortunately, the sun was not yet at its zenith in Saudi Arabia and she knew she wouldn't be able to sleep.

She was wrong, as so many travellers are, and slept through the two-hour helicopter journey out to the USS Westmoreland.

Sarah liked Captain Davis almost instantly, and a lot more than she liked Tsang or Barry. The last two both had goals involving victory, whatever that was, whereas Davis's goal was clearly the survival of his men. He reminded her slightly of her father too.

'How goes the day, Captain?' Tsang asked when they were all shown into the wardroom.

'Tolerable, Colonel,' Davis answered steadily. 'Now, what can I do for you ladies and gentlemen?'

'We'd like to harness your ASW equipment and techniques. Our mission is directed against a target currently sitting on the seabed directly below us -'

'What? Do you mean to say you've a rogue submarine out there?'

Tsang made a placating gesture. 'No. We have a downed vessel out there and we would rather it was not recovered by the people currently intending to use it. The problem is they may already be in the process of salvaging it.'

Davis shook his head. 'We'd have noticed any salvage operation going on here, Colonel. Fact of the matter is, there hasn't been anything bigger than a twenty-foot patrol boat out here all day'

"There will be,' Sarah put in. 'You'll know it when you see it.'

'Captain,' the intercom burst into life,' sonar. Contact reported at three thousand yards.'

'Contact?'

'We're running it on the computer now& Sound signature is probable Victor III.'

Echoing pings rippled though the Zhukov. 'Well,' Kutzov said fatalistically, 'I told you.' He nodded to another officer. 'Periscope depth.' He raised the periscope as the submarine shallowed and peered through it. 'American 'American cruiser cruiser Shit.'

Chiu turned to his attendant and whispered something in his own language.

"The surface vessel will be our biggest problem. The threat must be neutralised before anything else is done.'

The captain folded his arms. 'My government said to take you to these coordinates, but I will not go to war for you.'

"That will not be necessary'

"There are hundreds, thousands of people on that ship.'

'We mean them no harm. It will be necessary for us to take control of their flight-director area and command and control systems for a short period of time: until the Qe'shaal 's operational stability is assured and air supremacy established.'

The Russian captain snorted. 'If you think the Americans will let you, you're crazy'

"Then we will give them no choice,' Chiu told him. He tapped the side of his neck. 'Phoshaph siwo-roch. Nis'n qo wahlth'. He looked back to the captain.'Consider it done.'

Chapter Twenty-One.

Face to Face

Crewmen on the Westmoreland's deck ducked as something swept past, the air rippling. The ship was knocked cold and never even saw what had hit it.

In the CinC, every monitor and read-out went dark. Lights failed throughout the ship as fuses overloaded. Navigation, communications and weapons systems went down. All control systems for the ship's gas turbines failed simultaneously.

Ordinarily this would have meant panic, but here, the crew's reactions were silenced almost as quickly as their ship had been. A sickening wave of energy spread through the steel warren below decks, knocking people to the floor. Men and women simply tumbled into limp heaps wherever they were.

The ship was dead in the water.

Above the flight deck, two silver discs coalesced out of the blue sky. A moment later, figures stepped out of temporary red hazes in the cruiser's most vital areas.