The man stared at her, backed away. The 'policeman' grabbed him from behind.

'No it isn't me it's her it's no-o-o-.'

Catriona swallowed, looked through the windscreen and saw 'policemen' swarming out of the front of the headquarters building and along the wide pavement of the boulevard.

'Sorry,' she muttered, then stamped on the accelerator and pulled out into the traffic. She detested herself for leaving the little man behind, but she knew that she had no choice.

She steered the car through the traffic into the lane marked AEROPORT. I've got to get out of this b.l.o.o.d.y country, she thought.

Get to somewhere safe and tell everyone what's happening.

Before it's too late.

The Brigadier looked around the dusty tarmac for the last time, wiped at his face to remove the sweat and the ever-persistent grey flies. Everything was ready: the Hercules was fuelled up, Captain Yates and his men were on board. They had even managed to get a slot from Kebirian Air Traffic Control.

The Brigadier would have liked to delay their departure, but there was no arguing with the repeated direct order from the Secretary-General's office: ' Leave at once. We will make every possible effort to locate your Leave at once. We will make every possible effort to locate your Scientific Advisor, and pressure will be put on the Kebirians for Scientific Advisor, and pressure will be put on the Kebirians for leniency in the case of Miss Grant, but we repeat: for the present it is leniency in the case of Miss Grant, but we repeat: for the present it is imperative that you leave at once imperative that you leave at once.'

Yates waved from the top of the steps as the second engine fired, the huge blade spinning slowly and then speeding up. The Brigadier remembered the famous scene from the film Casablanca Casablanca and, not for the first time, found himself wishing that real life was as straightforward as the movies. and, not for the first time, found himself wishing that real life was as straightforward as the movies.

It was no good. He was being ordered ordered to leave. to leave.

'I'm sorry, Doctor,' he said aloud.

Then his eye caught a flurry of movement near the airport buildings, a few hundred yards away across the tarmac. He looked across, saw three of the local policemen and, standing between them, Jo and the Doctor. For a moment it seemed that they were all moving so fast that their limbs were blurred. An illusion caused by the shimmering heat-haze, no doubt, thought the Brigadier.

He started across towards them, wondering how he would manage to get Jo out of the hands of the local police. Perhaps he could bluff it, say that as a UNIT employee she had to be tried by an international court. It might work.

But even as he thought about it, he saw that the Doctor and Jo were walking towards him, clear of the police.

'Well done, Doctor,' he said as they approached. Did some fast talking again, did you?'

'You could say that, Brigadier,' said the Doctor.

The Brigadier turned to Jo. 'I have to say that I didn't believe it for one minute, Miss Grant. I know you would never kill anyone.'

Jo frowned. 'Believe what, Brigadier?'

'But surely you know!' He turned to the Doctor. 'Miss Grant's up for murder, according to the Kebirians.'

The Doctor smiled. 'Oh, don't worry about that, old chap. I think you'll find there's been a bit of a change of policy in Kebiria. Jo's perfectly all right.'

Nonplussed, the Brigadier looked from one to the other of them.

He half-expected Jo to giggle, but she didn't: she just stared into the distance, as if contemplating the horizon.

There was something odd about that stare, thought the Brigadier.

'Are you all right, Miss Grant?' he asked quietly.

'Quite all right, thank you, Brigadier,' replied Jo. But her eyes stayed fixed on the horizon.

'Well, we have orders to leave at once,' said the Brigadier.

'Good!' said the Doctor, rubbing his hands together. 'We've a lot to be getting on with in England.'

He and Jo set off for the plane. As they pa.s.sed, the Brigadier caught a whiff of perfume. Roses and cloves, it smelled like. Rich, cloying, expensive.

Funny. He wouldn't have thought Jo would have gone in for that kind of thing.

Catriona stared at the unmoving queue of traffic, at the blue-and-white striped barrier beyond it that marked the airport entrance, and clenched her fists in frustration. What was happening up there?

- if it's the aliens I'm finished it's too late I'm going to die like if it's the aliens I'm finished it's too late I'm going to die like Deveraux did oh Jesus someone help me I've got to get out of here Deveraux did oh Jesus someone help me I've got to get out of here - - With difficulty she controlled her panic, took several deep breaths, wiped the sweat from her eyes. She looked across the metal barrier at the road which led to the goods entrance, at the slowly moving line of trucks.

But they were at least moving.

She couldn't get the car over there, but if she got out of the car, she could thumb a lift perhaps.

Or just run for it.

She switched the engine off, pushed open the door, clambered out and over the bonnet, over the metal barrier. Jumped down on to the rough stone at the edge of the carriageway.

A horn blared: she ignored it, started running towards the airport.

Then the horn blared again, and Catriona heard the sound of breaking gla.s.s. She looked over her shoulder, saw a line of the 'policemen'

advancing along the highway on the other side of the barrier, walking over the roofs of the stationary cars. She saw a man dragged from his car, heard his screams.

Then, before she could think, the aliens were crossing the metal barrier between the two highways, jumping like gra.s.shoppers, their feet making chitinous clicks on the tarmac. Catriona aimed the gun at the nearest of them, pulled the trigger.

Nothing happened. She pulled the trigger again, heard a click.

Obviously the magazine was empty. She swore, hurled the useless weapon at the aliens, ran out across the road, hoping to put the stream of moving trucks between her and them. A truck swerved, almost hit her. She heard a crunch as it ran over one of the police, a squeal of brakes as it stopped.

Don't stop my friend for G.o.d's sake don't stop - - But there was no time to turn, to warn the driver. She had reached the verge on the other side of the road by now: ahead was a concrete embankment, topped by a mesh fence that marked the boundary of the airport compound. She glanced over her shoulder, saw people struggling out of their cars and trucks, running, grey-uniformed figures following them, making gra.s.shopper-like leaps across the traffic to pin their victims down.

She scrambled up the embankment, hooked her fingers into the mesh fence at the top. Through the netting, she could see a big Hercules transport plane, its engines running, slowly turning away from the airport buildings.

Catriona stared at it for a moment, at the RAF roundels and the blue logo just visible above the loading door.

- RAF thank Christ its got to be the UNIT plane Jo's people are RAF thank Christ its got to be the UNIT plane Jo's people are on there I can tell them what's happening what happened to her and on there I can tell them what's happening what happened to her and it's my only chance of getting out of this country alive I've just got to it's my only chance of getting out of this country alive I've just got to go for it go for it - - But the plane was taxiing away from her, towards the end of the runway. She knew that she had no hope of catching up with it.

There was only one thing she could do.

She clambered over the fence, catching her shirt on a jagged wire.

She struggled free, jumped down and started running down the main runway. The plane, perhaps a mile ahead of her, was turning slowly, readying itself for take-off. Catriona wondered how much runway a Hercules used. It depended on the load, she supposed. She carried on running, her shoes clopping on the tarmac. Sweat was trickling down her face.

The plane completed its turn, hung there, shimmering in the heat haze.

She wondered if they could see her. Surely they must be able to.

She waved her arms, pushed her hands forward palms first in a desperate parody of a 'stop' signal.

- they've got to see me they've got to stop please they've just got to they've got to see me they've got to stop please they've just got to - She wondered what would happen if they didn't stop. If the wheels missed her, would she be sucked up in the airflow, then dropped to bash her brains out on the concrete?

No, she was probably too heavy for that.

But she realized that, if they didn't stop, she'd rather be killed here and now by the plane. Rather that than be caught by the aliens. She remembered Anton Deveraux's scratchy whisper: '- dancing the code -'. Remembered the contorted face, the ruptured skin.

- I don't want to die that way, any way but that I don't want to die that way, any way but that - - The plane was moving, she realized. She could hear the roar of its engines as they throttled up.

- please they've got to stop please please they've got to stop please - - The plane was visibly bigger now, rumbling towards her. She ran faster, a head-down sprint of the kind she hadn't done since she was in school, keeping her eyes on the white guide line in the middle of the runway.

She wondered if she would feel the impact when the nose wheel hit her.

When the pilot put the brakes on, the Brigadier was almost thrown out of his straps. He glanced up at the Doctor.

'Looks like your change of policy didn't last very long.'

'Oh, I don't know, Brigadier. Perhaps the plane's got a flat tyre.'

But the Brigadier could tell that the man was worried. As the aircraft pulled to halt, he got out of his straps and strode towards the door. Jo followed him.

The door opened, letting a blaze of sunlight into the darkened interior of the plane. The Brigadier got up and walked to the door.

Outside a woman was shouting up at them. Her blonde hair was dirty, and her clothes were torn and bloodied.

'... aliens aliens!' she shouted.

'What's she talking about, Doctor?' asked the Brigadier.

The Doctor looked round, an irritable expression on his face.

'Nothing, old chap. Just some mad woman.'

'Jo!' the woman was yelling. '... believe me! JO!'

Jo turned and pushed her way past the Brigadier back into the plane. 'I don't know who she is,' she said, then hurried away.

The Brigadier frowned. He could see several policemen running across the rough ground between the airport buildings and the runway.

'I think we ought to investigate the situation,' he said. He looked over his shoulder. 'Benton! Bring two of your men and - '

'No!' said the Doctor. 'Wait a minute, Brigadier! That doesn't make any sense. This woman has been infected by an alien virus. Her continued existence threatens the lives of everyone on Earth. The virus may make her act irrationally - dangerously. We have to leave at once.'

The Brigadier frowned. He wasn't sure that the Doctor was making any sense. One moment the woman was 'just a mad woman'; the next she was infected with a deadly virus. And surely it was UNIT's business to deal with alien infections?

But then, the Doctor quite frequently didn't make any sense.

'The local police are aware of the situation,' the Doctor went on, as if reading the Brigadier's concerns from his mind. 'It's fully under control. I've given them plentiful supplies of an antiviral preparation.

We need to get to Headquarters as soon as possible to arrange for a worldwide immunization programme.'

The woman on the tarmac had noticed the approaching policemen now. She was glancing repeatedly over her shoulder, and almost screaming at them. 'Please! You've got to help! They'll kill me!'

'We'd better get down there, sir.'

It was Benton, looking over his shoulder. Captain Yates stood behind him, a frown on his face.

'No!' snapped the Doctor. 'If anyone goes down there without access to the antiviral preparation they will die.' The policemen had reached the tarmac.

'THEY'LL KILL ME!'.

'Far from killing her, Brigadier, they'll save her life - and ours, if I'm not mistaken. Now, please, we must leave at once.'

The Brigadier hesitated a moment longer. The policemen grabbed hold of the blonde woman, dragged her back across the tarmac. She screamed once, then struggled silently as they carried her away.

'You see?' said the Doctor. 'She's not dead.'

'I still think we ought to check - '

'Brigadier! They're immunized, you're not.'

The Brigadier looked at the policemen, now jogging back towards the airport building with the woman bundled onto their shoulders. He shook his head slowly, backed into the plane and let the Doctor shut the door.