Ed glared at Charlie across the table. Charlie glared back for a moment then lowered his eyes, looking shifty and uncomfortable. He knew Ed might be kicked out of the university because of his half-witted prank. Not funny and not clever as his mother would have said. Charlie was in trouble with Ed and if Ed decided to spill the beans, Charlie's troubles would know no bounds - not through this decade and possibly the next. He couldn't afford to be bull-headed about it with Ed. Ed wasn't mum. He wouldn't take any of Charlie's nonsense. He wouldn't hesitate to drop Charlie in it, if Charlie persisted in behaving like an arse.

Ed's problem began when his mother had to go up to Leicester to sort out some problem between his grandparents. Grandma was demanding a divorce apparently. So mum had asked Ed to take care of Charlie for a few days. The woman had no sense. Charlie was 13 chronologically but closer to 5 in his infantile sense of humour and under developed - no, scrub that - complete absence of any sense of responsibility. Ed was a serious, some would say humourless, 20 year old, coming to the end of his second year of a BSc in biology. He had neither the time nor the inclination to watch and round up Charlie for almost a week. Mother felt she had enough on her hands with her 'senile delinquent' parents, without Charlie taking every opportunity to increase the level of stress and drama. So Ed was saddled with the duty of policing his throw-back to the Bash Street Gang brother. What a drag. He tried hard for the first couple of days and gave Charlie a tour of the classes, labs, library, common rooms, campus grounds. There was no hope of getting the brat interested in anything for very long. He left him with some books, comics, puzzles and computer games and went off to his seminars, worried and depressed that Charlie was bound to have set fire to his room or broken his computer by the time he got back. In the event, it was a lot worse than that - though he didn't know it at the time. It was an entire week by the time he got the call to send his brother home, and he thought he'd got off lightly. Charlie had been remarkably quiet and well behaved. Or so it seemed.

As anticipated, Charlie had soon got bored with all the paltry entertainments laid on by old 'Gruntfuttuk', as he called his brother. It took less than a day of being left to his own devices and company to drive him to look for more extreme diversions. First of all, he just wandered about the campus looking for trees to climb. That form of recreation was soon exhausted though, as some park-keeper like individual in a peaked cap had got very shirty with him when he fell from about 20 feet onto a couple he'd been watching, canoodling below. He'd had a nice soft landing, but the couple were a bit bruised and shocked.

After that, he'd drifted towards the buildings, surveying them critically and wondering what they might offer by way of harmless amusement. He remembered something weird Gruntfuttuk had shown him in one of the labs and wondered if there would be anyone in there right now. Expressions of mischief and mayhem chased each other across his spotty features and he moved off purposefully towards the tall end building. Looking up, he saw the room was dark and there was no sign of movement within. Checking that nobody was watching, he proceeded to the entrance, decided to give the lift a miss and made his way up the stairs. Cautiously, he emerged from the stair-well onto the corridor and crept along to the lab of wonders to peep through the small rectangular window in the door. It was empty. He took a deep breath and carefully tried the door handle. It opened! What luck. He crept into the lab and surveyed the scene before him. All was still and quiet apart from some scratching and rustling coming from one of the cages. Drawn by the furtive sounds of rodent activity he walked over to the row of cages where he had seen the eerily glowing rats a couple of days before. They looked almost normal now, in daylight - just slightly green-tinged white rats. You had to see them in the dark to really appreciate how strange they looked.

Ed had explained that the guys in this lab were experimenting with a fire-fly gene that coded for the enzyme that made the little blighters glow in the dark. They'd found some way of introducing it into the DNA of the rats by using bacteriophages - a sort of virus that infects bacteria. It was all a bit boring and technical. Except the rats were amazing! They looked like little rodent ghosts in the dark. Ed had shown him the cabinet where the flasks of goo were stored that the rats were 'infected' with. He tore his eyes from the faintly green rats and looked over his shoulder at the cabinet. He blinked slowly, bit his lip, turned and walked towards the cabinet. It wasn't locked ...

That was a couple of months ago. It had been easy and it had been fun. He'd chosen a likely looking flask. They all had small alpha-numeric labels. He didn't have any idea what the labels signified so he'd chosen one that began ED - it had Ed's name on it. That was his twisted logic: "What's Ed's is mine and what's mine's my own". He smuggled it out of the lab, into Ed's room, into his knapsack and home. Couldn't have been simpler.

His first 'victims' had been the neighbours' cats. Several of them made use of the garden, making unspeakable deposits and killing birds. A saucer of milk placed where it couldn't be missed, laced sparingly with a couple of drops from the flask, was quickly consumed and had to be replenished three times. On Monday he took it to school and managed to escape from cross-country to get to the dining room just before all the rest. The jugs of water were all arrayed in four neat rows, ready to be placed on the tables, so he nipped over, took out his flask and poured just a small splash into each jug. He still had half a flask left but couldn't think of anything better to do with it than dispose of the evidence down a drain in the gutter outside the school and throw the flask into a hedge.

All he had to do then was sit back and await the results of his astonishing wheeze. The results took so long to appear that he began to think the flask must have been a dud. How disappointing. Then, when he'd almost forgotten about the whole thing, looking out of his bedroom window one night, he noticed a faint glow creeping across the garden. A cat! A ghostly cat! He gripped the window sill and gasped. It worked!

Over the course of the next week there was an uproar as glowing children, cats - a couple of hedgehogs even - but mainly children from Charlie's school were spotted towards the close of days, becoming more visible as the light faded. It seemed an epidemic though none complained of feeling ill. It took a while, but Ed finally put two and two together. Charlie's chums were aglow, a flask of phage, genetically modified with fire-fly DNA had gone missing from a lab Charlie had visited. What were the chances that Charlie hadn't pulled one of his puerile stunts? What were the chances that an investigation wouldn't lead straight back via Charlie to Ed, the lab of luminous rats and the missing flask? What if the glow was permanent?

These were the issues Ed was now taking up with Charlie. Charlie was wondering whether he should mention the half flask he'd poured down the drain. He decided things were already hot enough and if the glow did spread more widely, that would be the best time to confess: when there was no alternative - brave little chap. For the present, he said he was sorry and tried to look convincingly contrite.