4.

STALAGMITE CAVERN.

Amber put her hand to her head and groaned. 'Oh no. This is just brilliant.'

'She was in front of me when we came out of the narrow bit,' said Li.

Paulo splashed impatiently back into the cavern. 'I bet if we go back the way we came we'll find she's having a sit down.' But he felt guilty. Maybe he'd really upset her. Although there had been no other tunnels off the one they had just come along, there were numerous nooks and crannies. He peered into every one. Some were just small cracks when you got up close; some were big enough to crawl into.

The others followed. 'What if she's hurt herself?' said Alex. 'We're responsible for her. How could we have not noticed her dropping behind?'

'I think we'd have heard the screams,' muttered Li.

They were irritated, but they had to consider other possibilities. Getting a casualty out would be extremely difficult. And if she'd done more than just sit down, or gone back further than the last cave, she could be lost. How long would it take to find her?

Paulo emerged first into the stalact.i.te cavern. 'Tiff?' he called.

Amber came out next, then the other three.

They stood and listened for movement. The only thing they could hear was the steady drip of water.

Then a feeble voice: 'Help.'

It came from the tunnel they had abandoned.

The five friends exchanged weary glances. So she had decided to take the shortest route to the top and leave the rest of them behind. But she hadn't looked at the map: the tunnel wasn't just an easy stroll up to the ground, and now she was in trouble.

Paulo knelt down and shone his headlamp into the hole. He couldn't see anything, just the tunnel getting narrower and narrower. 'Tiff?' he called.

'I'm here.'

'Are you hurt?' he called.

'No. I can't get out.'

'Try coming backwards,' said Li.

'I have,' said Tiff. 'I'm stuck.'

Hex said in a low voice so that his voice wouldn't carry, 'Well, that serves you right, doesn't it?'

Amber nodded.

Li looked at Paulo. 'How narrow was it down there?'

'Just your size,' said Paulo.

Li gave him a long-suffering look. She took off her rucksack and handed it to him, checked the rope slung diagonally across her body, then got down on her hands and knees.

Without the rucksack she reached the narrow section in no time. She had to squirm along on her belly like a lizard. It was like climbing along the inside of a drainpipe. Her breathing echoed, emphasizing how tiny the s.p.a.ce was. She'd never been claustrophobic before but this was really unpleasant. She felt very alone. She kept reminding herself that her friends were back at the other end, friends who knew what to do if she got into trouble. The tunnel began to slope up steeply. She scrabbled to find handholds to pull herself up.

The tunnel suddenly turned downwards like an elbow. Li had visions of getting stuck round the corner. But Tiff had got through, so she could. In fact, thought Li as she squeezed around the gap, how did that little minx manage to get all this way? She must be tougher than she looks.

Li could see a ghostly white glow below her. A lamp. 'Tiff are you there?' she called.

'Yes.' Tiff's voice sounded shrill. Was she frightened? Good, thought Li. She deserves to be. Next time she won't go off on her own.

Li's headlamp illuminated a patch of brown mud as she inched her way down the steep tunnel. The floor was only a metre further down now. She vaulted lightly into the cave.

Tiff was sitting on the floor, her helmet off, looking miserable, but not injured it was her usual sulky expression. As Li looked around she saw a forest of big, jagged stalagmites, sticking up from the uneven floor like teeth in a shark's mouth.

For a moment she forgot that she was mad with Tiff. 'Wow,' she said. 'You've found a pretty amazing place.'

'Yeah, well, I want to go back now,' said Tiff curtly. She got up.

Li turned back to the tunnel to see how easy it was going to be to climb out. 'Did you try to get out?'

'Yeah. It's impossible.'

Li looked at her balefully. 'Well, I very much hope it isn't, or we're both stuck.'

Tiff jigged nervously from foot to foot. 'Come on, man, this is horrible in here. There's this noise.'

'That's not unusual in potholes,' said Li. 'It's probably underground water.' She inspected the tunnel. The first part was a slippery slope there were scuff marks where Tiff had tried to climb back up. Li was an experienced climber and could see tiny handholds but for Tiff it would be impossible.

A squeal interrupted Li's thoughts. She turned round sharply. 'What?'

Tiff's eyes were blazing. 'Did you hear it?'

And then Li made out a sort of chugging, booming noise. It wasn't water. It was regular, with a beat. In the toothy gloom of the cave, it was rather eerie. It surged, as though giving more power, then settled to a steady chug again. Like an engine.

'See?' Tiff was angry. 'You thought I was making it up. You people never listen.'

'I'm sure there's a perfectly normal explanation,' said Li. 'Or are you still frightened of monsters under the bed?'

Tiff looked at her with contempt. 'You should learn some manners. Remember I'm the customer.'

Li bit her tongue. 'I sense you have hostility issues,' she said. 'Maybe we should have a group hug.' Actually she would never do anything of the sort, but it was worth it for the look of revulsion on Tiff's face.

Li hopped up into the tunnel mouth. 'You stay here and I'll go up and throw you this rope.'

'You won't be able to climb out,' said Tiff scornfully. 'I kept slipping.'

But Li was already scaling the steep slope, feeling for tiny ledges with her fingers and toes. Slowly she made her way up to the elbow, then turned and threw down the rope for Tiff.

The sun was going down, splashing the sky with oranges, pinks and purples. Paulo and Hex were sitting on the terrace at the back of the hostel, watching an enormous display projected onto the white wall at the end of the building. On the display, three dots were moving around on a map like characters in a computer game. The dots were tracking devices which the group used on missions. Hex and Paulo had found some projection equipment in the hostel and improvised a way to enlarge the palmtop display to the size of a cinema picture. With the help of some up-to-the-minute phone technology they had reinvented hide and seek Alpha Force style.

Somewhere in the hostel, Alex was hiding. The others were split into teams, communicating via phones and hands-free cordless Bluetooth earpieces. Paulo was guiding Li in the house and Hex was guiding Amber. The winner was the first team to find Alex and take him prisoner. And it was getting very heated.

The boys spoke in low voices, their deckchairs just far enough apart that they couldn't hear each other. The projector was in between them, its whirring competing with the evening noises of crickets.

'Left, Li,' muttered Paulo, his eyes fixed on the screen. The hands-free headset was a small curl of silver plastic that hooked over his ear and rested on his cheekbone.

'Upstairs, first room on the left,' whispered Hex to Amber. On the screen he could see Amber was getting close to Alex, but Li was too. 'Hurry,' he urged. 'Li's in the next room.'

Alex's dot moved. He was getting away! Suddenly all the dots converged. From an open window on the landing came the sound of shrieks. The girls were giving chase.

It was too late for subtlety now. Paulo stood up and shouted encouragement at the screen. 'Go on, Li!'

Inside, Li saw Alex sprint for the stairs. Right, she'd head him off. The stairs went round and round, forming a square well. She vaulted over the banisters and dived for the lower handrail, catching it and vaulting over like a trapeze artist. In moments she was standing on the bottom stair looking up at Alex, the headset still in place, her phone in a zip pouch at her belt.

Alex's expression went through several very entertaining phases. First there was triumph as he pounded down the stairs, his feet a blur like a tap dancer. Then there was disbelief as he saw Li in front of him; then horror as he saw he was going to run smack into her.

Moments later he was tumbling over her back. She had ducked and rolled him over her. He curled himself into a ball to cushion his landing. Li put her foot on his chest, as though he was a lion she'd bagged.

Paulo raced in through the front door as Amber slid down the banister. 'Foul,' she called. 'Contestants aren't allowed to fly.'

'There are no rules about that,' panted Li. She took her foot off Alex. He sat up, rubbing his elbow.

Hex came in holding the palmtop, which he'd disconnected from the projector. 'That was just the beta test to iron out bugs. It doesn't count.'

'Rubbish,' said Paulo. 'We were victorious.'

Alex got to his feet. 'Let's see if Tiff wants to play.'

'She won't,' said Hex. 'She's watching a week's worth of EastEnders EastEnders on video.' on video.'

Alex got to his feet. 'It won't do any harm to ask.'

He made his way down the hall to the TV room and knocked, but there was no answer. Perhaps Tiff couldn't hear him: the sound was turned up very high. He opened the door and peeked in.

He looked back at the others. 'She's not there. And the window's open. She's left the TV on and scarpered.'

'Hex?' called Amber. 'Need some magic here.'

Hex went into a small room off the main corridor. It was the hostel office. A filing cabinet was open and Amber sat at a desk looking at the addresses of all the kids who had been on the course the previous week, including their mobile numbers.

'I just called Tiff's mobile and she's engaged. See if you can trace her.' She pulled the Bluetooth headset out from behind her ear and put it on the desk.

Hex got out his palmtop. 'No problem.' Amber pushed her phone across the desk. Hex read the number off the display and typed it in. 'Just finding her network now... Keep phoning her in case she ends her call.'

Hex could only trace her as long as she was using the phone. It was illegal, of course, and well beyond most hackers, but Hex was in a league of his own. There wasn't a firewall he couldn't slip past, a pa.s.sword he couldn't crack. Now he was in the computer belonging to her phone company. Mobile phones were a good way to track somebody because they only worked if they were near a transmitter, or cell. Hex just had to find out which cell was taking her signals at the moment. It wasn't as accurate as the tracers Alpha Force wore, but it would narrow her position down to within a hundred metres or so.

Amber put her phone on the desk. 'The signal's gone. She's switched it off or gone out of range.'

Paulo and Alex came in with the projection equipment and laid it carefully on the floor.

'Doesn't matter,' said Hex. 'I've got her.' He turned his palmtop round. 'Find that grid reference.'

Li plucked an Ordnance Survey map from the bookshelf. She spread it out and located the co-ordinates. 'Hex, are you sure?'

Hex glanced at her impatiently. 'Transmitters don't lie.'

She looked up at the others. 'It's a disused railway tunnel.'

Amber frowned. 'What on earth's she doing there?'

Alex got down to practicalities. 'Do we take the Range Rover or the quad bikes?'

Paulo looked a bit sheepish.

Li glared at him accusingly. 'You're not still tinkering with the Range Rover?!'

Paulo looked pained. 'There's something a bit dodgy with the ignition system. You know I like to have things perfect.'

'Quads it is,' said Alex.

5.

THE R RAILWAY T TUNNEL.

Three quad bikes spun gravel. Then the fat tyres bit, and they zoomed off the drive and bounced up into the moorland.

Hex, in the lead, pushed the bike up to top speed, keeping a careful eye on the ground. Amber, on the seat behind him, was in charge of the palmtop, navigating as straight a route as possible to the tunnel. As well as being a powerful computer the tiny machine was a global positioning system or GPS, using military satellites to pinpoint their position anywhere in the world. Paulo and Li followed on another bike and Alex was on the third.

But a 'straight' route didn't mean straightforward. The riders constantly swerved around clumps of heather, rocks and gullies. At a top speed of fifty-six kph, if the quads. .h.i.t an obstacle they would turn over.

Amber nudged Hex in the ribs and he adjusted the bike's course. Beyond the pool of light given out by his headlamps the night was pitch black. A railway tunnel, Amber thought. What was Tiff doing there? She must have gone to meet someone. What kind of trouble could she be getting into?

A glow of light was growing in the distance. At first she thought it was reflected headlights from a road: surely they'd vanish again. But they didn't. The area of light became bigger. She looked at the palmtop. 'That's it,' she hissed in Hex's ear.

Hex slowed. The others braked. There was a cl.u.s.ter of arc lights, and figures moving around. Something was going on there.

Paulo stopped. 'Let's leave the bikes and go in on foot.'

They cut their engines. They expected silence but instead there was a noise. A rhythmic thumping.