The Doctor fished in a pocket for the key to his private lift to the ground level. The TARDIS key was next to it on the ring, and he kept it in his hand.

The lift took a few moments to reach him and chimed when it arrived.

Before the Doctor could step into it, he heard the unmistakable sound of a gunshot from along the corridor. Forgetting the lift, he started towards the mezzanine.

Major Barry just wanted to keep things calm. The guard and the other intruders made for a tricky situation where a lot of people could get hurt, and that was the last thing he wanted.

The guard had shouted to them to put down their guns. If it were only his own team he'd have done so, but he daren't give that order when he didn't know how the other guys would react.

It took some effort of will not to comply with the guard's orders, and he thought of asking the other intruders to join him in obeying them.

Then the guard's throat exploded in red, the colour of the gunshot that filled the computer suite. Barry looked for the source and saw one of the other intruders, back near the door they had come in through, turn his gun towards the UNIT team.

A gun with a smoking muzzle.

A willingness to kill, which was now being turned against his people.

Then it was too late to back down.

Tom just wanted to keep things calm. A quiet B and E, grab the data he wanted and get out. The other intruders made that more problematic, but it was the guard who really screwed things up. Tom could see how easily this could all turn sour, and that was the last thing he wanted.

The guard had shouted to them to put down their guns. If it was up to him, he'd have done so, but he couldn't do that when a group of paramilitaries - terrorists? - with automatic weapons were breathing down his neck.

Then the guard's throat burst in a red summer bloom.

For an instant Tom felt a moment of supreme calm; his blink was a frame holding a cluttered picture in eternal grace. With a bang, the moment was gone as completely as if it had never been, and the air was ripped to shreds in a roar of automatic gunfire and flying metal.

Tom leapt for cover, firing in the general direction of the enemy as rapidly as his index finger would flex. You didn't dodge bullets; they moved too fast. But everyone in the building saw it as bullet-dodging when they bolted in the hope that their enemies couldn't shoot straight. And indeed they couldn't, as they couldn't aim properly while darting around.

Major Barry raced for the protection of a tiled pillar while Clark laid down suppressing fire. 'Who the hell are they?' he asked, when he got his breath back. 'Intelligence said the building was guarded by a handful of college kids with six-shooters, not a SWAT team.'

'Intelligence couldn't find their asses with both hands, you know that.' Clark thumbed new shells into her shotgun. 'It's probably the usual crap somebody was told something by somebody who said he knew somebody who saw what was going on, and automatically assumed it must be true.

Next thing you know, he's convinced everybody even though he was never there to see anything. Bloody pillock. I wonder if it's too late to get a transfer to the UNIT marching band.'

'You create it, and I'll make sure Tsang transfers both of us.' He motioned to a couple of men on the far side of the mezzanine, indicating for them to go round and outflank the opposition. We'll make up the percussion section.' He rolled out, opening up with three-round bursts, while Clark blasted chunks of plaster from the walls above the enemy's heads.

Tom covered his head with his arms to protect himself from flying plaster and glass. Whoever these people were - and it seemed obvious to him they must be security - they were pinning him and his team down for a reason, probably a flanking movement.

What surprised him most was the sophistication of the weapons. He had expected the building's guards to have pistols and maybe a shotgun, but this lot were armed to the teeth with the latest military hardware. Something was seriously wrong, but he had no idea whether he would survive long enough to find out what it could be.

Out of the corner of his eye, Tom saw someone pull the pin on a grenade and start to swing it towards him. He scrambled backwards, as if he could outrun it, firing instinctively. An explosion split the air, shredding the thrower, and Tom belatedly realised he'd hit the grenade instead of the man.

The two guards the UNIT team had chained up were in the unlit stairwell that led from the lift-maintenance floor above the penthouse to the roof.

They had been cuffed to the railing with their hands behind their backs, but they weren't taking it calmly.

Both men had been struggling violently against their bonds, hoping against hope that something other than their wrists would give.

One of them finally got lucky, not by managing to pull free but by getting his shoe off. He had been almost paranoid about being locked into his handcuffs ever since the practical joke the other guards had played on him as an initiation rite. Since that embarrassing day, he'd kept a spare key in his shoe.

He slid the shoe across to the other guard who managed to flip it into the ir with a kick. The first guard twisted aside as the shoe hit the rail, and the key dropped into his hands. In a moment, he was free.

The second guard gestured with a flick of his head. 'Get onto the roof and use your mobile phone. See if you can get hold of Tse Hung or Yue Hwa.

Tell them what's happening.'

It was nightmarish, not a bullet ballet.

Says UNIT'S Sergeant Gibson: 'At first, it was just like training at the killing house: acquire targets, get the job done and watch your mates'

backs. But once people got hit hit I'd never seen a dead body before. I mean, I'd seen a lot of fights, and people cut and smashed, but not dead. When he falls against me I'm, like, knocked down. It was like getting hit by a side of beef. Then I realise that that's blood on my face, and in my clothes, and he's not breathing. I mean, I'd know if he was, because we were all shaking with every breath, and there was nothing from him. Just nothing. Then I got as far away from him as I could, because I didn't want a dead guy touching me.' I'd never seen a dead body before. I mean, I'd seen a lot of fights, and people cut and smashed, but not dead. When he falls against me I'm, like, knocked down. It was like getting hit by a side of beef. Then I realise that that's blood on my face, and in my clothes, and he's not breathing. I mean, I'd know if he was, because we were all shaking with every breath, and there was nothing from him. Just nothing. Then I got as far away from him as I could, because I didn't want a dead guy touching me.'

Another debriefing went: 'The weirdest thing was, I couldn't hear a thing.

Don't get me wrong. The place was noisy as hell -guns, explosions, screaming and dying but but I dunno, it was like the whole thing was so loud you just didn't register it as sound any more.' I dunno, it was like the whole thing was so loud you just didn't register it as sound any more.'

Tom Ryder told it his own way, on his taped debriefing. 'Jesus, why couldn't they have just kept the hell out of the way? We could all have walked right out of there, if they had any damn sense. I mean, better them than me, but but Half of me says the bastards deserved it, but the rest of me just wishes I hadn't had to do some of those things.' Half of me says the bastards deserved it, but the rest of me just wishes I hadn't had to do some of those things.'

Tom had run a gauntlet of flying lead trying to get at the computer with the disk in it. It would contain all the data he wanted. Why else would these others be there, if not to either remove the evidence or steal it for themselves? Either way, that disk had to become his.

Glass walls and plaster partitions exploded into dust. Monitors burst with big enough pops to make them breakdance on their desks. Gunmen ducked and leapt, slid and ran, all the while releasing hell from their hands.

Then, in the midst of it all, somehow audible even over the gunfire, the Doctor's bellow cut across the battleground.'STOP!'

The UNIT pilot had kept the Blackhawk orbiting the Pimms Building as instructed, waiting for a signal from the major or Captain Clark.

So far there had been no radio traffic, but now he noticed movement on the roof. He couldn't tell who it was, but it looked like a man in uniform.

Assuming it was one of the team in need of pick-up, the pilot started swinging around.

The silence - apart from the crackle of flames and the hiss of the sprinklers - was sudden and shocking. The Doctor was standing in the centre of the mezzanine, near the lifts, wreathed in smoke. "There has been enough fighting! Put your toys away and let me explain things to you.'

Tom had to admire his bravery. The guy was walking out of the smoke and fires like some Old Testament prophet, heedless of the fact that either side might want to blow him to hell. No wonder Sarah thought so highly of him.

Russell Barry nodded in silent satisfaction. The Doctor had chosen the wrong side this time. The choice probably wasn't deliberate, but it wasn't up to him to judge the man. Either way, he was a security risk.

'No, Doctor. Your operation here is being closed down. Don't make us think you've finally changed sides.'

'There are no sides,' the Doctor snapped back. 'Just right and wrong, and if you want to call those sides then I suspect we're all on the same side.'

'Speak for yourself. We're not the ones consorting with hostile aliens or running Triad gangs. We're not running drugs or guns. Can you say the same?'

'I can explain the situation to you. Typical human, always making snap judgements without knowing the full facts. Can't you people just grow up?'

'Arrogance will get you nowhere, Doctor.'

The guard was dialling frantically, but not getting through. To his annoyance and embarrassment the illuminated display on the phone told him it was out of credit. He was searching in his pocket for a credit card to top up the phone when the down-draught from a swooping helicopter knocked him flat.

When he picked himself up, all but giving up on trying to work out what was happening to him, he saw the chopper hovering a few feet above the gravelled roof. A man in flying gear was framed in the side door, beckoning to him.

The guard thought that perhaps someone else on duty had sounded the alarm and this was a police chopper. He ran and leapt to catch a rope that hung from its door.

He heard a 'What the hell -' from above, and realised that the man who had beckoned was now looking startled. He'd obviously been expecting someone else. By now the chopper had sideslipped away from the building, and the guard hung on over a drop of several hundred feet to the ground.

'It's one of the guards,' the co-pilot yelled from the door. The pilot cursed and immediately started swinging the helicopter around. This helped the uniformed security guard who had only managed to climb halfway up the abseil rope. The pitch rolled him in through the door of the chopper and he knocked the co-pilot flying.

The co-pilot came to rest against the back of his seat, firing his pistol back into the passenger cabin, but the guard was sliding around so much because of the chopper's tilting that hitting him was impossible.

The pilot tilted the helicopter's nose forward just as the guard lunged and slammed into the co-pilot, grappling with him for the gun. The gun went off again, but the guard deflected the co-pilot's arm and this time blood erupted from the pilot's chest.

'Shit!' the co-pilot yelped. He tried to regain control, but the pilot had slumped onto his own controls and the helicopter simply flipped. Neither the co-pilot nor the guard had time to try to escape as the rotor blades slashed into the building's roof.

'Oh shit,' Julie Palmer muttered, surely echoing the sentiments of everyone who was looking up at that moment.

UNIT'S helicopter had finally given up its attempt to stay airborne. The rotor-tips hit first, smashing through the roof of the tower and sending glass fragments scything downwards. Then the fuselage was through, and the whole ceiling had turned into a storm of razor-edged rain.

The wrecked helicopter plunged down through the tower, its spinning rotors creating an indoor tornado that burst mirrored windows as it spiralled around. When the chopper reached the mezzanine levels it managed to drag Clark, screaming, over the edge to follow it down. Palmer managed to hang on, but could feel her fingers slipping.

With a painful rip her fingernails gave way, and her heart thudded into her throat as she lurched down. Then something locked round her wrist, almost pulling her arm out of its socket.

It was the Doctor, lying on the floor with both hands around her wrist. 'Hold on,' he grimaced. Too terrified to think of anything else anyway, Palmer let him haul her up, pulling her ankles clear just in time as a rotor flashed past within an inch of them.

When the Nighthawk hit the stone garden an instant before Clark, it smashed through into the service areas in the basement, and imploded in a tangled heap. The building juddered to its very roots as the helicopter was swallowed whole by a growing dragon of igniting fuel, and the tower became a chimney for Clark's crematorium.

'Arrest him,' Barry shouted, but Palmer's mind wasn't back on her job yet.

She was just too glad to be alive.

"Thank you,' she managed to say.

The Doctor tipped his hat and grinned. 'My pleasure.' His expression became more serious. 'Tell Colonel Tsang that she needn't worry. This will all be over soon.'

'What?' But he was departing.

'Doctor, you're under arrest. Stop or I shoot,' Barry yelled. The Doctor kept going. Barry started shooting from across the floor, and the Doctor started running.

The Doctor vaulted the stairs, descending rapidly. Barry and a couple of other soldiers who had followed his lead in opening fire dashed to the edge, waiting for the Doctor to re-emerge on the ground floor.

They laid down concentrated fire when he appeared, churning up the stone garden as the Doctor bolted across it, bullets nipping at his heels.

Then he was inside the police box in the far corner. A second later, it began to emit a strange trumpeting and faded from sight.

Terrified, pumped up with adrenaline, Russell Barry was jumpy and unpredictable, his instincts operating far faster than his thought processes.

So the Doctor had run away. Well, that was fine with him. Unfortunately the gunshots had reignited the firefight.

It was only a matter of time before the UNIT forces won. He knew that because they were trained for it. He didn't know who the others were, but they clearly weren't a military force trained in special weapons and tactics.

When a head wearing a black Balaclava landed beside him, he pushed his pistol muzzle into the mystery' man's throat, and almost gagged as his own throat received a similar threat. He kept his eyes locked on the other man's, watching for a flicker that might indicate a trigger being pulled. From this angle, he couldn't see the man's hand and watch the tendons on his finger.

Not daring to breathe, the two men lay at arms' length, their bodies stretched out in opposite directions.

'Who are you?' Barry asked carefully.

'Who the hell are you?' was the only reply. The accent was American, and Barry realised that the eyelids he could see through the Balaclava were dark. This man was black, not Chinese. Maybe he wasn't one of the building's guards after all. Curiouser and curiouser, Barry thought.

'You're not the building's guard,' he said.

'Neither are you.'

A heartbeat of searching for a way out alive. 'Cops?'

'Not exactly' The pressure on Barry's throat never wavered, and he had no intention of moving his own pistol. 'You?' the man asked.

'Not exactly. UNIT'

'You're with UNIT?' The mask was unreadable, and then Barry heard the slight creak of a pistol's hammer being eased down. The mystery man held his gun clearly away. 'Perhaps we've been working on the same case from opposite ends. Tom Ryder, CIA.'

Barry thought he should have guessed. He took his pistol away from Tom's throat and breathed a lot more easily. 'Only the CIA would be so bloody stupid.' He and Tom issued ceasefire orders on their throat-mikes at the same time.

'We're not the ones who came in armed for Desert Storm II.' Tom stood as the gunfire fell silent.

'We're the ones who came prepared for anything, up to and including an extraterrestrial military force.'

'You're not serious?'

Barry sighed. 'We seem to be the only ones who are.'

Chapter Eighteen.

True Colours of a Hero

Flames gave an extra boost to the pre-dawn light as Tse Hung watched the firefighters trying to control and contain the blaze at the Pimms' Building.

'I can think of no music that would soothe a heart burned by these fires,'

Chiu said.

Tse Hung was surprised to hear the ersatz Chinese say something like that. Normally he was taciturn and businesslike, displaying no soul. The remark wasn't much of a silver lining, but Tse Hung would take it. Besides, only Chiu could transport goods the way the Tao Te Lung had been doing.