An explosion shook the ground; Oakley almost lost his grip on the phone. He glanced over his shoulder at the bunker, saw flames and smoke. Swore.

'Kelly!' he bawled into the phone.

Silence.

He cleared the line, dialled oh-one-oh.

The line crackled, buzzed.

Oakley waited. Ahead of him the tanks were rolling forward, sunlight gleaming off their chitinous armour. A section of fence a few hundred yards ahead of him exploded into flame: Oakley heard a man scream, saw him running, burning.

Napalm, he thought. Jesus H Christ, where did they get that idea?

The phone crackled, then a voice spoke. 'Carver here.' The line was surprisingly clear: Oakley imagined the white-uniformed man standing on the bridge of the Eisenhower Eisenhower. Imagined the key in his hand, the red box chained to the bridge controls.

There was another explosion of fire, near enough for Oakley to feel the heat on his face. He estimated the interval between the two impacts, the range of the weapon, the speed of the approaching tanks.

The next one would get him. There was no time to think about it - he just had to do it. To say it.

'It's Oakley, sir,' he said into the phone. 'The code is - Tripwire.'

'Tripwire,' said the calm voice. 'Confirmed.'

Then there was an explosion of flame and light and pain, and the phone was wrenched away from his hand.

Oakley's last thought before the darkness descended was quite simple: we're going to get you for this. we're going to get you for this.

Thirty.

'Brigadier, sometimes I think your grasp of practical temporal physics is somewhat limited. If we're all blown up by an H-bomb whilst I'm trying to repair the TARDIS navigational circuits, how can I possibly go back in time afterwards and stop it from happening?

Besides which, the old girl's rarely on target at the best of times and I can't take the chance of anything going wrong. There's no way I'll ever repair the Prognosticator, you know.'

He made it sound as if this last was the Brigadier's own personal fault. The Brigadier decided to ignore the remark.

'If you say so, Doctor,' he said. He picked up the phone Osgood had wired to the remains of the lab circuits, dialled nine; jiggled the handset against the rest then put it to his ear. The line remained dead.

'But the fact remains that the telephone lines from this building are down, the radio room appears to have been eaten by our Xarax friends, and quite frankly the quickest way you're going to get a flight to Kebiria at the moment is to go to Heathrow and thumb a lift.'

The Doctor shook his head, glanced at the huge face of the Xarax queen. It twitched its antennae and dribbled a little honey onto the floor.

'Wait a minute!' He set off out of the lab at a run. The Brigadier shrugged to himself and followed.

He caught up with the Doctor in the car park, interrogating a bewildered Sergeant Benton. 'Are you quite sure you haven't seen any cars here?'

Benton shook his head. 'Not one, Doctor. We a.s.sumed - '

'Never mind what you a.s.sumed!' He turned swiftly. 'Brigadier!

Have you checked the garages yet?'

'The garages? Not yet, but I'll - '

'Never mind,' said the Doctor again. He started across the tarmac at a run. Again, the Brigadier followed him, wondering what on Earth the Doctor wanted a car for. He could hardly drive to Kebiria.

He found the Doctor standing outside the open door of the concrete sheds where the troop transports were kept. Inside, instead of the usual canvas-covered trucks and trailers, was the sleek, gleaming black shape of a rocket plane.

'What the blazes is that doing in there, Doctor?' asked the Brigadier. 'It's meant to be a top secret -' He broke off, as he realized that the plane had eyes.

The Doctor advanced towards the plane. Its eyes examined him as he advanced, then the shutters clicked shut over them. A tiny pair of jaws unfolded and a proboscis reached down. The Doctor produced a beaker of honey, let the creature taste it. 'I knew that they had to be using the metal for something,' he muttered, apparently to himself.

A door opened in its side, grounded with a thud. The Doctor hastily clambered inside.

The Brigadier rushed up to him. 'Hold on a minute, Doctor. You're not - '

'You can't come with me, Brigadier, there isn't room and there isn't enough fuel.'

The Brigadier looked inside, saw the Doctor crouched inside the - you couldn't really call it a c.o.c.kpit, it was more like the creature's mouth, or even its stomach. Slimy green tentacles were wrapping themselves around the Doctor's neck.

The Brigadier remembered his earlier doubts. His hand moved towards the holster of his gun. 'Doctor, are you sure you're going to be in control of this - this thing?'

The Doctor glanced at him, smiled. 'I'm going to have to be, Brigadier. There isn't really any choice.' He paused. 'I suggest you take cover. Even though this is only a copy of a rocket, I suspect that lift-off will be pretty violent.'

Then the door flipped upwards, shutting the Doctor inside. The creature began a hissing sound, which gradually increased in pitch.

The Brigadier ran to the side of the garage, crouched down behind a workbench.

A few seconds later the Xarax began to roll out of the garage. It had barely cleared the door when there was a deafening explosion.

The Brigadier sprang up, ran through the clearing smoke.

He was just in time to see the black shape of the alien disappearing into the sky on a tail of flame.

'Well, Doctor,' he said. 'Good luck.'

He almost added, I hope you know what you're doing; but it was a bit late for that.

THE NEST IS UNDER ATTACK!.

Jo struggled to respond to the situation. She wanted peace -

- of course she wanted peace she wanted the nest to shut down of course she wanted peace she wanted the nest to shut down that was what she was here for that was what she was here for - - - but there were missiles approaching.

ACT NOW!.

She released the instructions to the rocket planes, and they steered towards the incoming missiles. She judged the distances from their radio and radar signals, realized that there was no hope of intercepting all of the missiles except by crashing into them.

You will have to die for the nest, she told the planes; and received their joyful acknowledgements.I - this isn't right I'm supposed to stop all this I'm supposed to be this isn't right I'm supposed to stop all this I'm supposed to be here to here to - - More missiles came from the west. More rocket planes needed to be despatched. Jo instructed them to send details of the missiles'

construction, to disable one for a.n.a.lysis if possible.

Weapons must be met with equivalent weapons, until there was peace.

From the bridge of the USS Eisenhower Eisenhower, the Kebiriz coast was a smudge on the horizon, brown beyond the blue of the sea. The bow of the vessel pointed directly at the coast; the white painted lines on the flat grey deck seemed to be aimed at it, like sighting lines for an oversize gun.

Admiral Kent J. Carver of the US Navy stared at the scene for a moment, and wished it had been that easy. He shook his head, turned to the Eisenhower Eisenhower's captain.

'Missile status?'

The captain didn't glance up from the radar screen. 'They've all gone, sir. Intercepted, every single one.'

'Anything coming in?'

'Plenty.' The captain glanced up for a moment. 'If they keep this up we aren't going to be able to hold them much longer. They'll be all over southern Europe by tonight.'

Carver looked away from the man's eyes. Looked out to sea for a few seconds.

It all looked so peaceful. So - He saw the moving dots a second too late. They were skimming the surface of the sea, below the level of radar. He opened his mouth to speak, to warn the captain, but was beaten to it by a brilliant flash of light at the bows.

The blastproof gla.s.s held, just. Carver saw cracks in it, then focused on the ruined bows beyond, the buckled deck.

Every alarm on the panel shone a red light; somewhere, a klaxon started to sound. Next to him, the captain began bellowing orders into a microphone.

Carver walked away, across the deck that was already canting to one side. He knew that there was nothing to stop the aliens putting a nuclear warhead on their missiles next time. They'd been given a more than adequate supply.

There was only one course of action left.

But it wasn't up to him to decide on it.

He picked up a red telephone handset on one side of the bridge, ignoring the men racing round him, the shouts about firefighting crews and evacuation procedures. He took a key from his pocket, inserted it in the panel to which the handset was connected, put the handset to his ear.

The phone at the other end rang once, then a woman answered.

'Pentagon Navy five?'

'Carver here,' said the Admiral quietly. 'Put me through to the President. Now.'

Thirty-One.

Jo's legs were cramped with constant kneeling and the skin of her face was crawling with sweat, but she couldn't let her concentration slip now.

She felt, rather than saw, the new missile coming in on its unusual trajectory over Europe. It was slower than the missiles from the ships, and there was something odd about its radio signals - '- honey honey good good sweet sweet honey to be honey dancing honey honey good good sweet sweet honey to be honey dancing to be sweet sweet to be sweet sweet - ' - '

It was Xarax.

- that means the Doctor's lost or he never got there and the Xarax that means the Doctor's lost or he never got there and the Xarax have taken over England as well it's all over all over unless I can have taken over England as well it's all over all over unless I can persuade the defenders to destroy the missile persuade the defenders to destroy the missile - - - after all it might be dangerous - - yes make the Xarax turn on themselves yes make the Xarax turn on themselves - - She issued the instructions: new missile is dangerous is fake Xarax will destroy nest destroy honey no dancing no honey no sweet sweet - Jo watched as the defenders closed in on the missile. She could almost hear the Doctor's voice: 'This ought to confuse them.'

For the first time in hours, she smiled.

The phone on the Brigadier's desk made a few awkward, experimental tinkling noises. He s.n.a.t.c.hed up the receiver, was immensely relieved to hear a dialling tone.

'Good old Osgood,' he muttered as he dialled the emergency MoD number.

The phone was answered at once.