Then the bucket crashed down over her head. Drops of liquid spattered over the uniform, over the stone floor. The woman dropped to her knees, and Jo hit her again, then pushed the bucket down over her head.

The gun crashed, bucked in the woman's hand. Catriona thought she heard a bullet whistle past her ear, certainly heard a dull crack of broken plaster.

There was an instant's absolute, terrifying, silence. Then, slowly, the woman collapsed. Her gun landed on the concrete floor with a clatter of metal.

Jo vaulted over the body, ran through the door. Shaking a little, Catriona gingerly picked the gun up and looked out through the doorway. Jo was standing in the middle of the corridor, staring at her.

There were two more guards racing towards her, pistols in their hands. Without thinking, Catriona raised her own gun. They both saw her at the same time, stopped, turned to aim at her - - there's no need to shoot them no need to shoot anyone just tell there's no need to shoot them no need to shoot anyone just tell them to drop their guns them to drop their guns - - But Catriona's finger curled on the trigger.

The gun seemed to explode in her hand and she almost dropped it.

One of the women staggered slowly backwards, a startled expression on her face. She aimed the pistol, but her hand started to shake. She dropped it, fell sideways, her entire body twitching as if there were a damaged motor in it.

- Jesus Christ I've killed her I've b.l.o.o.d.y killed her Jesus Christ I've killed her I've b.l.o.o.d.y killed her - - She turned to the other guard, half expecting to see the gun aimed at her, half expecting the force of a bullet to knock her back against the wall. But the woman was stepping back, her hands shakily raised, her head turning from side to side in terror. Suddenly she turned and ran, her footsteps echoing on the stone.

Catriona turned to Jo, who had picked up the dead guard's pistol and was holding it out towards Catriona.

'You'd better have this - I mean - you seem to know how to - '

Of course I don't know how to, thought Catriona. I don't even know why I picked the thing up, I just pulled the b.l.o.o.d.y trigger by accident, I didn't even know it was happening and Jesus Christ I killed her Jesus Christ I killed her and I don't want to have to do it again, not ever, not under any circ.u.mstances, so just take that thing away from me - and I don't want to have to do it again, not ever, not under any circ.u.mstances, so just take that thing away from me - But she said nothing, just held her hand out. Jo plonked the gun in it, managed a shaky grin as Catriona took a grip on the weapon.

'We'll need the keys,' she said, looking over Catriona's shoulder.

Catriona turned, saw the bunch of keys still hanging from the door where the first guard had opened it. She stepped over, took them.

Shoes. They had to have shoes.

She looked down at the second guard, who was lying still in the corridor, with more blood than Catriona would have believed possible pooling around her chest.

'b.l.o.o.d.y h.e.l.l,' she muttered, then closed her eyes for a moment. She found herself wondering if perhaps there was a G.o.d after all, and if so what He would have to say to her about this.

She opened her eyes, put the gun down. Her fingers shaking a little, she began fumbling with the laces on the dead woman's shoes. They were shiny, black, flat-heeled. Policewoman's shoes. Surprisingly, they were too small for her. She flung them across to Jo, who stared at them for a moment, then slowly began to put them on.

Someone was shouting in the distance.

Quickly, she turned to the first guard. She was lying still in the doorway, with the bucket over her face. Catriona suddenly realized that she might be dead too, or dying. She had an absurd impulse to check the woman's pulse. Instead she pulled off the woman's shoes, pushed them on to her feet. They were too big, but she laced them tight.

Footsteps were racing across stone, doors clattered, more shouts.

'Shouldn't we take their uniforms?' said Jo. 'Then we could - '

'No time,' said Catriona. She started running, the loose shoes flopping on her feet so much that she began to wonder if she'd have been better off without them. They ran past a line of cell doors, towards a barred door. Catriona looked at Jo.

The younger woman tried several of the keys, finally found one that fitted. As the door opened an alarm bell started to ring. Catriona stepped through the door, found herself in another corridor with barred cell doors. She swore, glanced at Jo.

'Left or right?'

Jo hesitated. A guard appeared at the end of the corridor to the right, shouted something which was inaudible over the bell. Jo ran: Catriona followed her, expecting at any moment to feel a bullet shatter her shoulder blades.

'Halt!' A man's voice. 'Halt now or we will shoot you!'

Jo stopped, looked around wildly, dived to one side. Catriona saw a cell door set into the wall, the young woman wresding with the bunch of keys. She wondered why on Earth Jo was trying to get in to a cell, but before she could catch up with her and ask there was an explosion of gunfire. Catriona tried to drop flat, only got as far as her knees.

Then her body seemed to freeze. Behind her, over the sound of the bell and the humming in her ears, she heard booted footsteps approaching, echoing off the steel doors of the corridor.

'Put your hands up!' said the voice.

Catriona tried to move, couldn't. With an effort, she managed to lower the hand carrying the machine pistol so that the weapon pointed at the ground.

'Throw the gun down! NOW!'

She tried, but she couldn't let go. Her fingers wouldn't respond to the commands from her brain. She tried to speak, to say she couldn't move, couldn't let go of the gun, but her mouth only produced a faint croak, like someone moaning in their sleep. Cold metal touched the back of her neck.

She tried to think, a last thought, a last story, anything that would make sense of her dying, but all she could come up with was I killed I killed her. I killed her. And now I'm going to pay. her. I killed her. And now I'm going to pay.

Seven.

With a final thud, the TARDIS materialized in the darkened laboratory. After a moment, the door opened, and the Doctor stepped out. He switched the lights on, then sat down in a chair, facing the door, with a slight, confident smile on his face.

Thirty seconds later, the Brigadier came in.

'Right on time, old chap,' said the Doctor.

The Brigadier stared at him.

'Osgood said the place was empty.'

'That's because it was, until a few minutes ago.' The Doctor stood up and put his hands behind his back: his 'lecturing position', the Brigadier sometimes called it. 'I've repaired and calibrated the Personal Time-line Prognosticator. It predicted that you would be here at 4.42 a.m. It's now 4.43 and you arrived about half a minute ago. That's a fairly low margin of error, wouldn't you agree, Brigadier?'

The Brigadier stared at him.

'Doctor, you don't want want it to be true, do you? You don't want me to gun down you and Jo, here in the laboratory?' it to be true, do you? You don't want me to gun down you and Jo, here in the laboratory?'

The Doctor shook his head. 'It doesn't have to be in the laboratory.

As I told Jo, it could be anywhere, anywhen. And no, of course I don't want it to happen. There is even a small chance that it won't happen. I just want to make you aware of the facts.'

The Brigadier looked uncomfortably away. 'I am aware of them, thank you, Doctor. And I have taken what steps I can. Now, can we deal with more immediate matters?'

'Jo has been arrested in Kebiria,' said the Doctor.

'How on Earth do you know that?'

'My dear fellow, you don't think I haven't used the Prognosticator to track Jo's movements as well? Last time I checked on her she was in a prison cell in Kebir City with another woman and as far as I could tell from reading their lips they're planning an escape.'

The Brigadier considered this for a moment. 'I don't think that's wise. I've already got somebody from the Secretariat on to this, they should be in touch with the Kebirian government first thing in the morning.'

'Yes, but Jo doesn't know that. I think it would be easier if I went and collected her, don't you?'

The Brigadier stared at him. 'Collected her? In that thing?' He gestured with his swagger-stick at the TARDIS. 'I thought you never knew where you were going to end up?'

The Doctor frowned severely. 'It's not quite that bad, Brigadier. I've just had a little difficulty getting used to the navigational systems again.' He paused, glanced down at a key that he was holding in his hand, frowned. 'Anyway, this should be easy enough. I've linked the Prognosticator to the primary s.p.a.ce-time orientation circuits. All I have to do is work out where Jo will be in - say - ten minutes, and the TARDIS will take me there. Then, if you'll be kind enough to sit here for the next twenty minutes, I can use a fix on you to return here.'

He started towards the TARDIS, the key in his hand.

'Just a minute, Doctor,' said the Brigadier. 'Are you telling me I've got to sit here for the next twenty minutes whilst you swan off to Kebiria in that thing?'

'That's right, Brigadier,' said the Doctor over his shoulder, opening the TARDIS door. 'Twenty minutes.'

The door closed.

'But Doctor - '

The TARDIS began to issue the wheezing, grating noise which the Brigadier recognized as being a prelude to dematerialization. The light on the top flashed. The wall became visible beyond the machine.

It had almost vanished when there was a m.u.f.fled thud, like distant thunder. The TARDIS winked in and out of existence, appeared, wraith-like, in several different parts of the room at once. Then there was another much louder thud and a gust of wind hit the Brigadier in the face as if something had exploded. Automatically he threw himself flat on the floor, covered his eyes. There was another loud bang, followed by a strangulated trumpeting noise: the Brigadier looked up, saw the TARDIS back in place. Before he could react, the door flew open and the Doctor emerged in a cloud of smoke, coughing. From within the TARDIS there was a hissing sound, and the smoke issuing from the door thinned and then stopped.

Too late. Quite a lot of it had acc.u.mulated under the lab ceiling.

A bell began ringing, painfully loud in the small room. A red light flashed. Somewhere in the distance, a siren started to blare. Cold water began showering down over the lab, and the lights went out.

The Doctor ignored all of this, just looked around, then down to where the Brigadier was slowly picking himself up, trying not to think about the dry-cleaning bill for his uniform.

'On the other hand, Brigadier,' he said sheepishly, 'perhaps we should take a plane, if you would be good enough to arrange one.'

Jo stared at the man, and the man stared back at her. He was an Arab, tall and lanky, his face burned and wrinkled by the desert. He was wearing a frayed denim jacket and loose jeans; his feet were bare.

'Are you a prisoner?' asked Jo, feeling that it was a silly question even as she asked it. She looked at the bunch of keys in her hand. She had a ridiculous notion that she ought to apologize to the man for barging into his cell without knocking.

'I have that misfortune,' said the Arab, in slow, careful English.

'Can I help you?'

'We're - trying to escape,' said Jo, glancing over her shoulder at the corridor outside. She heard a man shouting.

The man got up, walked swiftly past her to the cell door, peered out. Jo started to follow, but he held up a hand, shook his head.

Suddenly, he was gone.

There was a scuffle, a crash of gunfire. Jo ran forward, saw Catriona standing over the body of the guard, splashes of blood staining her shirt. More blood leaked from a neat line of holes in the man's back. The prisoner was looking up and down the corridor, holding the guard's machine pistol.

He turned, smiled at Jo.

'My name is Abdelsalam,' he said. 'Follow me.' He began to run lightly down the corridor.

Jo looked at Catriona, who shrugged. 'No choice, I suppose,' she said. Her voice was shaking.

They set off after Abdelsalam, caught up with him by a locked door. 'Come on Jo, do your stuff,' said Catriona.

Jo swallowed, worked the lock. Catriona pushed the heavy door open. Abdelsalam jumped through, gun at the ready, but there was no one there. An empty corridor faced them, of the familiar design.

Abdelsalam ran down it, shouting, 'Vincent! Belqua.s.sim!'

There were shouts from several cells. Abdelsalam listened, then ran to one and beat on the door. Jo joined him, frantically examining the keys. The wailing of sirens drifted in through the door, accompanying the continuing clamour of the alarm bell in the women's block.

'Quickly!' said Abdelsalam.

The first key Jo tried didn't work. The second jammed in the lock.

Jo looked around frantically.

Abdelsalam put the muzzle of the gun against the lock. 'Stand back,' he said quietly. 'And pray to Allah.'

He fired, twice.

The door opened.