'Yes, that should do it,' muttered the Doctor. He adjusted the screwdriver: there was a brief, loud whirring sound.

The floor tilted, rolling Jo off her feet. She saw Zalloua with a hand clutching a bundle of broken piping, struggling to keep his balance.

He shouted, 'This is worse! Reverse what you have done, Doctor.'

The Doctor took no notice. 'Close your eyes, all of you, and roll into a ball. It'll help.'

'What do you mean?' asked Benari, who was also struggling to stand. Parts of his jacket were slimy and smoking where the acid had burned them.

'I've made it think we're indigestible, so it's trying to excrete us,'

said the Doctor. 'Make yourself as small and frictionless as you can, you'll make things easier for it.'

'But -' began Jo. Before she could complete the objection, a shower of cold, stinging fluid washed over her. She pushed her head between her knees, closed her eyes, felt herself sliding across the lurching floor. She banged against something, rebounded, skidded around, felt the skin of her face stinging. Instinctively she put her hands up to further protect her eyes.

Then she was falling, rolling down a long wet channel. She hit something hard, cried out; for a moment she was falling freely. Then she landed on a damp, soft surface. After a moment, she heard another body land beside her. She opened her eyes, saw the Doctor and, behind him, Benari hanging six feet above her on the lip of the jaws of - the jaws - The jaws were at least thirty feet across, and above them towered a chitinous face the size of a large house. Antennae sprouted on top like small trees growing from a wall. The body behind it heaved up, cathedral-sized, under the dark roof of the nest chamber.

'Doctor!' shrieked Jo. 'It's enormous!'

The Doctor sat up, turned his sightless eyes in the direction of the huge face. 'Now steady on, Jo. It will be big. We were inside its body, remember, and only a small part of it at that.'

As he spoke, Zalloua appeared inside the huge mouth. He stood up, stared out past the Doctor and Jo. 'We have to regain control!' he shouted.

Jo looked over her shoulder, and saw why he was shouting. The nest defenders were advancing towards them from all sides, their jaws open.

Zalloua pulled out a gun, fired at one of the defenders. It didn't even stop.

Jo pulled the Doctor to his feet. 'Doctor! We've got to run!'

She led him away, ran into a phalanx of advancing defenders, turned - Too late. She felt the long jaws close around her.

She smelled roses and cloves.

She screamed.

Twenty-One.

'Greyhound to trap seventy-four. Greyhound to trap seventy-four.

Come in, Rashid.'

The Brigadier tapped his swagger stick against the map on his knee, scanned the darkened landscape below.

Nothing.

He pushed the radio switch to 'receive', but heard only static.

'Where the h.e.l.l are they?' he snapped.

Yates, piloting the helicopter, pointed down at the shadowy desert.

A smudge of light moved slowly across the landscape; after a moment the Brigadier realized that it was a plume of dust, dimly illuminated by the light of the moon.

He glanced at his watch: six-thirty local time. About half an hour till dawn.

'Well, they'd better get a move on, or they're not going to get to the nest before it's light,' he said.

'I'm not sure it's them, sir,' said Yates.

'Eh?' But the Brigadier was instantly alert. True, he was expecting the enemy in the air more than on the ground; a squadron of Harriers were on watch around the nest, and Americans had carrier-based fighters on standby in the Gulf of Kebiria. But the Brigadier had insisted on Rabat sending ground support. He wanted to destroy the nest, but he wanted to do it carefully.

He wasn't going to risk killing the Doctor and Jo again.

If he hadn't already killed them, that was. He still hadn't heard from Moore.

He shook his head. No point in worrying about that now. He got out his binoculars, tried to focus on the blur of dust. He thought he saw something that might have been a jeep; but on the other hand it might have been anything.

He opened the radio mike again. 'Greyhound to trap forty-one. Do you read?'

'Trap forty-one,' came the crackly response from the Harrier squadron leader. 'Are you seeing what I'm seeing?'

'Dust devil at -' the Brigadier looked at the map '- November hotel zero-six-five?'

'That's the one. Want me to go down and take a look?'

But before the Brigadier could reply, flickers of light burst out around the dust cloud.

Muzzle flashes.

'Or perhaps I'd better not,' said the voice of the Harrier pilot.

The Brigadier changed to the UNIT emergency frequency. 'Trap seventy-four! Rashid, do you read me?'

There was a loud explosion, and the helicopter slewed sideways.

'What the -?' said Yates. He yanked at the stick, pulling the chopper into a steep climb. 'I thought these fellows didn't have any anti-aircraft capability?'

There was another explosion, a little further away this time.

'They don't,' said the Brigadier. 'Or at least, they weren't supposed to.'

The helicopter lurched again, and the airframe began to shake in a way which the Brigadier knew probably meant trouble. Yates wrestled with the stick, cursed as the chopper went into a slow but accelerating descent. He glanced over his shoulder at the Brigadier.

'We've lost the fuel line, sir. Get ready for an emergency landing.'

A Superhawk and a helicopter in less than forty-eight hours, thought the Brigadier. If I get out of this alive, the Minister's going to have my hide.

The radio crackled and bleeped: the Brigadier opened the switch.

It was Butler from the Harrier. 'Trap forty-one to Greyhound. You all right down there, sir?'

'We may be out of the game,' replied the Brigadier, watching the darkened desert rising towards him. He took deep breath. If the aliens had anti-aircraft capability - Then he was going to have to knock the nest out. Now. No questions.

Sorry, Doctor, he thought. If you're in there. If I haven't already killed you. And sorry, Jo.

The ground was getting closer. Fast. Too fast.

He glanced at Yates, who was still wrestling with the controls, but knew better than to break his concentration.

'Butler,' said the Brigadier at last. 'I want you to go for the alien construct - fire at will, flatten the thing if you can. Don't give them any chance to return fire.'

'Will do. Good luck, sir.'

'Thank you, Butler,' said the Brigadier. 'We're going to need it.

Over and out.'

Tahir heard the helicopter's motor stop, and half a minute later the sound of the impact as the craft hit the ground. He looked up, struggled to find the crash site, but the moonlight wasn't bright enough for him to see clearly.

Suddenly there was an explosion of light. Tahir covered his eyes against the glare, but it was too late: the after-images on his retinas told him he'd lost a precious half-minute of night vision, maybe longer.

'We should go and help them out,' said Jamil, next to him. Jamil was one of Vincent's men: a keen, young, Libyan-trained killer.

Vincent was ahead somewhere, with the first wave of men who were supposed to blow a hole in the nest wall. Tahir had a feeling that Jamil had been left back to keep an eye on him.

'The ones in the helicopter are beyond help, I should think,' he observed. He risked uncovering his eyes, saw only a dim flickering of flames. He reckoned that the site of the crash was at least half a mile away.

There was a distant stutter of gunfire.

'There are others!' said Jamil eagerly. 'They are still fighting!'

'We have no idea of the numbers and I'm not even sure which side is which,' said Tahir. 'If you think you can work it out, go ahead. I suggest we stick to our planned mission. Vincent won't be pleased if his back-up goes off chasing another battle.'

Before Jamil could reply, there was a brilliant flash from the direction of the alien tower, followed quickly by the roar of an explosion. The sequence was repeated three times; only when the echoes of the last explosion had died away did Tahir hear the sound of jets, see the three exhaust flares curving away against the dark sky.

He scowled. As soon as they'd heard the sounds of tanks and armoured personnel carriers moving across the desert, Tahir had argued that they pull out; but Vincent had insisted that they continue.

'We don't want the United Nations claiming credit for our victory, eh?' he'd said. But it was now becoming increasingly obvious that Vincent had made the wrong decision. Tahir knew that it wouldn't be the first time that had happened.

'Come on, then,' said Jamil. 'We follow Al Tayid Al Tayid.' He got up and climbed across the rough rocks, giving orders to his men as he pa.s.sed them. They jogged towards the nest, the metal petrol canisters strapped to their waists making them look as if they were aliens themselves.

Tahir frowned. What was the GAF man doing? Did he think that those explosions had been Vincent's work? Surely it wasn't possible that he had failed to see the jets? It would be suicidal to take those men in. Ahead, the mound was a shadow against the mountains; in the half-darkness it was impossible to tell how much, or how little, the missile strikes had damaged it.

'Wait!' Tahir called. 'The planes might come back!' But he had left it far too late. Jamil was beyond hearing.

He stood up, gazed around him, tried to make a sensible a.s.sessment of the situation. But before he could think, bright yellow light flared above him. Tahir looked up, saw a cloud of burning fuel that, a few seconds before, must have been a jet aircraft.

The light from the explosion shone on the blue-black carapaces of hundreds of Xarax helicopters as they dropped out of the night sky towards him.

The Brigadier clutched at his ankle and wished he'd taken up the opportunity of a refresher course in helicopter emergency escape procedures. He'd always thought it was a case of 'if in doubt, jump'.

But no doubt it mattered when you jumped, he thought.

He had a feeling he'd jumped a few feet too soon.

'Are you all right, sir?' came Yates's voice from somewhere in the darkness.

'I've sprained my ankle, cricked my back and I've got a hole in my arm which seems to have opened up again under the strain of impact,'

said the Brigadier irritably. 'Otherwise I'm quite well, thank you.'

Yates appeared over the top of a rock, his face dimly lit by the flames from the wreck of the helicopter. The Brigadier struggled to get up, winced as he put his weight on his injured ankle.

Yates came down and helped him up. As he stood, he saw a flare of light from the direction of the nest.

'Looks like Butler's lot have got to work, sir,' observed Yates.

The Brigadier grunted, shook his head. 'I just hope that the Doctor and Jo aren't in there, that's all.'

'Jo?' asked Yates, glancing at the Brigadier sharply. 'I thought she'd escaped from prison. She could be anywhere.'

So could the Doctor, thought the Brigadier.