Students remaining: 36

Sophie Clarke (Girl #11) gazed out of the bus window and sighed. If the rest of the trip was going to be like this, she would sooner turn round and go home; at least it would be better than spending the weekend hiking through the pouring rain. It had started raining heavily shortly after the bus left Parkwood Comprehensive School and it hadn't let up since. "Good thing I packed my anorak," she said to her neighbour, Benita Wright (Girl #18). "Looks like I'll need it."

Benita and Sophie had been friends all their lives, having grown up in adjacent streets. Physically, they were very dissimilar - Sophie was slim, fair-haired and blue-eyed, whereas Benita was a slightly plump black girl - but that had not stopped them from bonding over their dolls when they were three years old. Now, thirteen years later, they were still friends and they planned to remain so for the rest of their lives. They even had matching silver pendants which proclaimed this fact, two small discs etched with the words: Friends Forever.

"It might stop before we get there," said Benita, who was a natural optimist. She opened her hold-all and pulled out two packets of crisps. "Want a snack?" she asked, offering one of the packets to Sophie.

Sophie took the packet (prawn cocktail flavour) and opened it, as Benita opened her packet of ready salted. As the two friends sat munching their crisps, Sophie gazed round at the other thirty-four students on the bus.

Across the aisle from herself and Benita sat Shane Grantham (Boy #9) and Daljit Sandhu (Girl #9); there had been rumours lately that there was something going on between those two. But, if there was, it would be a while before they deposed Michael Walker (Boy #3) and Lauren Hunt (Girl #1) as 11G's Number One Couple. The pair in question were in the seat second from the back in the same row Sophie and Benita were in and they hadn't stopped holding hands since the bus left.

At the very back were the members of the nearest thing Parkwood had to a gang: Devon O'Hare (Boy #2), Liam Selby (Boy #6), Adam Martin (Boy #8), Daniel Gifford (Boy #13) and Theo McKenzie (Boy #17). These five were rarely seen apart and had been quick to commandeer the back seat, much to the dismay of their form tutor, Mrs Holton, who thought they were the rowdiest boys in the class and put at least one of them in detention every week. Earlier, she'd had to put a stop to their horseplay by threatening to make them move to the front of the bus where she could keep an eye on them.

The warning seemed to have had an effect because Sophie hadn't heard a sound from them since. In fact, she realised suddenly, the whole bus was strangely quiet. If you got thirty-six teenagers together in a group, they invariably made at least some noise no matter what sanctions any adults present threatened them with. But all the noises which usually accompanied a party of students on a school trip had disappeared, replaced by the sound of . . . snoring? Sophie turned to Benita to confirm it and saw her friend slumped in her seat, fast asleep. The packet of crisps she had been eating moments before had spilled unnoticed over the floor.

And it wasn't just Benita. Shane and Daljit were asleep in their seat across the aisle, as were Jonathan Hill (Boy #7) and Antony Cartwright (Boy #12) in the seat immediately in front of Sophie and Benita. In fact, Sophie realised with growing alarm, everyone on the bus (at least those in her immediate vicinity) seemed to be asleep - and she was feeling tired herself, even though it was only three o'clock in the afternoon according to her watch. What was going on here? It was almost as if there was some sort of gas coming through the bus's air-conditioning system. Maybe if she closed the vents above her seat . . .

She did so, but it didn't seem to make a blind bit of difference. If anything, she felt more tired than she had before. And she was also frightened; something told her she had to get out of here fast. She reached forward and shook Benita by the shoulders. "Benita!" she called. "Benita, wake up! We've got to get out of here!"

Benita did not respond, except to grunt in her sleep. Sophie realised it was up to her; she was the only one who could get everyone out of this. Luckily, she and Benita were sitting right under the emergency hammer which was used to break the windows in the event of an accident. It was all she could do to stay focused long enough to climb out of her seat, apologise to Benita as she trod on her foot and reach towards the hammer. Or where the hammer should have been . . .

Because, directly under the sign that said: Emergency Use Only there was . . . nothing. The hammer which should have provided her with a means of escape was missing. It was risky to jump out of a moving vehicle, but she would rather take her chances doing that than end up falling asleep like her classmates. She could not explain it, but something told her that no good could come of this. For one thing, why would they gas everyone for no apparent reason? And why would they remove the emergency hammer? It was almost as if someone didn't want any of the thirty-six students to escape.

That was the last coherent thought Sophie had before she too was overcome by the gas and slumped to the floor. The bus, bearing its unconscious passengers, continued on its way, heading down narrow country lanes. Only the driver, wearing a mask to protect himself from the gas he had released, knew its final destination. And he also knew that thirty-five of the students on the bus would never see their families again.