Kerstin shrugged. 'I don't know. I only come here on holiday.'

Fitz stood up, stepping into the clearing.

A hand on his shoulder. 'What are you doing?' said Kerstin in a panicky whisper.

'They've been in there for ages. I'm just going to have a peep inside.'

Fitz left the safety of the trees and walked over to the cabin. It looked neat and compact, its wooden walls painted the usual rustred. He walked around it, discovering a grimy window on the far side. Holding his breath, Fitz peered through. In the gloom he could just make out the far wall, and a blocky shape in the middle. As his eyes adjusted he saw it was a table. Of the three men there was no sign.

He walked back round to the door, giving the handle a tug. It was locked. He knocked, heart hammering in his chest, ready for flight.

But there was no answer. It was as if the men had vanished, as if the cabin was some sort of TARDIS.

He heard Kerstin run across the clearing and turned to her.

'Do you want to bring them back out?' she hissed.

'There's no one in there,' said Fitz.

Kerstin stared at the door as if she expected it to burst open at any moment. 'Well, where did they go?'

'That's what I want to find out. Now help me bust this door open.'

It took several attempts, but between them they forced open the door by repeated kicking that Fitz feared would attract unwelcome attention. But at last, after a hefty kick from Fitz, the door crashed open.

Fitz went in first, hoping Kerstin wouldn't notice how scared he was. The cabin was hare, and Fitz relaxed.

'No danger here,' he said, turning round to her and smiling widely.

The interior was dusty and dim, with a few shelves and a workbench at one end, a chair and table in the centre. There was no other exit apart from the door.

Kerstin followed, her trainers making no sound on the wooden floor. 'What now?'

She looked as if she was about to suggest going to the police again which, Fitz realised, was the sensible thing to do. 'Find out where they went,' he said lamely.

Kerstin walked around the shack. 'This is a dead end,' she muttered.

Fitz walked up to the workbench. There was a vice clamped to the side of it, and Fitz idly toyed with the handle. As he did so the floor gave a jolt beneath them. Fitz gave a yelp of surprise and grabbed on to the workbench, exchanging a panicky look with Kerstin.

Then he noticed that at the bottom of the walls was a lengthening strip of concrete. It took him a moment to figure out what was going on. The floor of the shack was descending. The whole thing was a lift.

'Well, now we know how they got out,' called Fitz above the noise of the engine. He watched fearfully as they descended into the shaft, its concrete walls streaked with oil, the ceiling of the shack receding above them. The table and chair were juddering about with the motion, Kerstin trying to still them.

At length the far wall gave way on to an open corridor, brick-walled, concrete-floored and lit by dim bulbs hanging from a concave ceiling.

They stepped out of the lift. Fitz's heart was thumping in his chest and one look at Kerstin told him that she was feeling the same. 'Don't suppose Bjorn knew about any of this,' said Fitz.

Kerstin smiled thinly. 'Suppose not.'

Fitz sighed. Anything was possible. This pa.s.sage probably led to the cavern of some exiled alien dictator, or the underground base of an alien advance force.

And they were walking right into it. What the h.e.l.l was he doing?

They went a little way along the corridor. It smelled of oil and cement and neglect. Fitz expected to b.u.mp into the white-suited chaps at any moment, but the place was deserted. Presently they came to a metal door, covered in peeling green paint. It was ajar and he gave it a gentle push. It swung open to reveal a large area which looked like the changing rooms of a football club. There was a row of showers at the far end, lockers and benches. Slung on to hooks on the wall near the door were half a dozen of the white biohazard suits, the silver helmets stowed on a shelf above them. The perfect disguise.

'Come on,' he said to Kerstin. 'Put one of these on.'

Kerstin's eyes widened. 'Are you mad?'

Fitz took one of the suits down and handed it to her. 'Totally and irretrievably.'

The Mantises had started chittering and struggling to escape the moment they'd left the golden sky-sea. Sam looked out of the slit-window to see that they were now floating through the middle of a cavern with a floor of undulating red rock dotted with stalagmites. Jagged stalact.i.tes hung down from a low ceiling. It was like flying inside the mouth of a giant monster. The whole place was lit by a distant pink sky-sea.

The flyer spiralled down towards the far end of the cavern, away from the sky-sea. Sam frowned. There was something there. A blackness which was hard to look at. It seemed to draw her mind out through her eyes.

As they grew nearer, the Mantises became more and more agitated.

She felt a gentle b.u.mp as they landed in a shallow bowl of dusty red rock near some stalagmites which towered twice the height of their dirigible. Beyond them, dense, impenetrable blackness.

One of the frog-things appeared before her, bearing a trident as tall as itself. The tendrils binding her fell limp and retracted. Other frog-things herded the Mantises from their seats and out through a hatch in the side of the dirigible.

The eyes of the frog-thing before her were wide, their lids almost invisible white lines against the pale-green skull. Its mouth was gaping and Sam noticed with a slight sense of disgust that it was drooling, thick strands of saliva running out of its round red mouth and on to its brown leaflike garments.

She was hauled roughly out of her seat and pushed down a ramp on to the dusty cavern floor amid the Mantises, which were now screeching in abject terror. Sam grimaced in anger. They were manhandling her as though she were a sack of spuds. And she wasn't going to take it any more.

She made to clamber to her feet, ready to fight the creatures off and make a run for it, but the b.l.o.o.d.y Mantises were clawing at her jeans, their spiky limbs drawing her down with them.

Unable to resist, she was herded towards the row of stalagmites which loomed before the blackness. Two of the frog-things were drooling over the gla.s.sy red rock, thick mucus pouring from their mouths in streams.

Sam was lifted up and taken to one of the stalagmites. They pressed her against the side that faced the black wall. She wriggled, but her back, legs and neck were becoming stuck to the rock, her feet a whole metre above the dusty ground. She felt them grab her arms and dribble all over them, sticking them to the side of the stalagmite. She saw that they were doing the same to the Mantises, which had kept up their unearthly screeching.

The frog-things let go, and Sam struggled but she couldn't move her arms or her legs, or even her head. The mucus had hardened and held her as fast as superglue.

And before her the strange blackness. It had the quality of a swarm of flies, its edges indistinct and blurry, and it was spreading over the rocks, advancing towards her.

'Hey!' yelled Sam, her voice rising in fear. 'Let me go!'

The frog-things had prostrated themselves in front of the blackness, all six of them, their arms and heads raised towards it, a slow moaning wail rising from their throats.

She suddenly realised what was happening. This was a sacrifice. They were going to sacrifice her, and themselves, to this unknowable blackness.

She struggled anew, but it was no use.

All she could do was watch, her only movement her terrified thumping heart, as the blackness closed in on her.

Chapter Ten.

A Means to an End Professor Nagle observed the Doctor's reaction through the two-way mirror. It was interesting. He had jumped up when she'd first spoken, his look of surprise changing to a scowl of righteous anger. When she'd asked for his help his long, handsome face had adopted an expression of almost comical surprise.

'Help you?' came his voice through a speaker on the monitoring desk. 'Help you?' He stepped right up to the gla.s.s. He really was a looker, and his strange clothes only went to accentuate his good looks. The way his hair curled above his forehead so naturally would have looked like an affectation on anyone else. The refined, epicurean set of his mouth, those intense eyes. you?' He stepped right up to the gla.s.s. He really was a looker, and his strange clothes only went to accentuate his good looks. The way his hair curled above his forehead so naturally would have looked like an affectation on anyone else. The refined, epicurean set of his mouth, those intense eyes.

He was ranting on now about being shot and imprisoned. Nagle exchanged a grin with Lindgard. She enjoyed being in this position of power. They could see the Doctor, but he couldn't see them.

She leaned forward and pressed the b.u.t.ton that activated the mike. 'Doctor, your att.i.tude isn't helping either of us. If you calm down, I'll explain everything.'

She heard Lindgard catch his breath. 'Is that wise?'

She switched the mike off. 'Probably not. But we've come as far as we can. The Doctor really is our last hope.'

Lindgard frowned. 'If you're sure. But you really will annoy Major Wolstencroft.'

Nagle grinned. 'So what?'

'OK,' said Lindgard, smiling back at her. There was no warmth in his expression. 'Play it your way.'

'I will.' She turned back to the Doctor. He really was no use to her in there. 'Doctor, I'm going to come in through a door to the left of the fireplace. Please stand well back, with your arms by your sides.'

The Doctor did as he was told and stood beside the sofa, a feeling of expectation and relief surging through him. At last, freedom of sorts, though he supposed they weren't going to let him go just like that. This Professor Nagle certainly sounded civilised, though he didn't let his guard drop for a second.

Sure enough, a door opened to the left of the fireplace. The Doctor mentally kicked himself for not noticing it before. Through the door came a pet.i.te woman in a crisp white lab coat, her shoes tapping on the floorboards. She was smiling, showing perfect white teeth.

The Doctor didn't smile back. Instead he walked right up to her. He was a good head taller. 'You know, I loathe pastel colour schemes. Bland. Boring. Soul-sapping.'

Her smile wavered, but only slightly. She had a pale, long face, and wore round gla.s.ses. Her brown hair was tied back in a ponytail. Streaks of grey put her age somewhere in the mid-forties. 'Hey, I'm sorry about all this,' she said, waving a dismissive hand at the soft furnishings. 'It's our interview room.'

'I know a euphemism when I hear one,' said the Doctor. 'Why am I being kept here?'

The woman shrugged. 'We had a bit of clearing up to do. At the farm. We had to put you somewhere.' She was observing him closely, as if he were an interesting though slightly disturbing painting. 'You are are the Doctor?' the Doctor?'

The Doctor folded his arms. 'I am indeed. The definitive article.'

She smiled and extended a hand. 'I'm Professor Jennifer Nagle.'

The Doctor took her hand. Her eyes were sharp and green. Her gla.s.ses magnified them, something the Doctor always found slightly unsettling.

The Doctor opened his mouth, closed it again. What to ask first? Probably best to start with the basics. 'I have some questions I want answered. Now. Such as, what exactly is this place? What are you doing here and what have you done with my friends?'

Nagle looked surprised. 'Friends?'

'Back at the farm,' said the Doctor. 'There were two people with me. A young man called Fitz and a young lady called Kerstin. I didn't see what happened to them after your cronies shot me.'

'Ah,' said Nagle, glancing back through the two-way mirror. 'I guess they must have gotten away. No one else was brought down here.'

'Down here?' said the Doctor. He'd guessed from the air pressure that they were some distance underground. And he'd only been unconscious for about an hour, so they must still be in Sweden. 'So we're beneath the forest?'

'Yes,' said Nagle. 'This is a former nuclear shelter we purchased from the Swedish government.' Her smile was beginning to waver and signs of agitation were showing in her face. 'Doctor, I must know if you are going to help us. There's not much time.'

'I can't help you if I don't know what's going on!'

'OK,' said Nagle. 'Follow me.' She turned and walked out of the plush prison cell.

The Doctor followed, eager to be out of confinement. She led him into a monitoring room, in which a fair-haired man with a retrousse nose sat behind a desk.

The Doctor recognised him at once. 'Dr Lindgard, I presume,' he said coldly.

Lindgard stared back, his face blank. 'I see you have recovered, Doctor. I am glad.'

The Doctor rubbed his chest. The pain was still throbbing like a wasp sting. 'If you wanted my help, you should have asked me. There was no need to shoot me!'

Lindgard blinked. 'We couldn't be sure you would agree to help.'

The Doctor whirled round to Nagle. 'Oh, so we're up to something dodgy down here!' he cried. 'No doubt you're responsible for the disappearances, and the appearance of those creatures which attacked the farm. And the disappearance of Johan's body!'

Lindgard and Nagle were staring at him. He realised he had been shouting. 'Well?'

Lindgard shifted in his seat. 'Mr Svensson's body was a biological hazard. We have it here under observation.'

'And the creatures which hatched from him? I'd like a closer look at them.'

'All in good time,' said Nagle.

'I take it you are not the State Biohazard Protection Unit.'

Lindgard smiled thinly. 'That was just a cover for our operation here.'

The Doctor was getting tired of Lindgard's supercilious manner. 'Well, don't keep me in suspense who are you?'

Nagle's face was serious, her green eyes wide behind her gla.s.ses. 'You may have heard of us before. We're a section of C19.'

'Ah.' C19. The part of the British government that funded the UK arm of UNIT. In return, they took possession of all the alien technology UNIT left behind. And they did dangerous, unethical things with it. 'So why are you, an American, and you ' he pointed at Lindgard 'a Swede, working for the British government?'

'Exploiting alien technology for the furtherance of humanity,' said Nagle, her eyes gleaming with evangelical zeal. 'Nationality doesn't come into it. I worked for UNIT for years, before C19 requisitioned me for this job. The same with Boris.'

The Doctor narrowed his eyes at Nagle. 'How exactly does abducting innocent people and causing plagues of vicious aliens contribute to the furtherance of humanity?'

Nagle and Lindgard exchanged a look.

Nagle took off her gla.s.ses and started cleaning them with a cloth. 'There were teething problems...'