IT WASN'T really a time machine. Not your usual time machine with all those flashing lights, where you sit in a chair and turn up sometime else. The world had obviously moved on since H G Wells's day.

"It's in this lorry," said Professor Anstruther, slapping the side of the truck with the flat of his hand. It made a dead, slightly hollow sound, as if the metal sides of the vehicle were several inches thick. Sue stood in the staff car park at the university and looked up at it. She'd seen this plain white-painted truck parked there, outside a doorway marked 'Temporal Physics'. It had been there for months, becoming part of the scenery. It didn't have 'Time Machine' painted on the sides.

"Why build it in a van?" Sue asked, still awed by the size of the thing close up. "What was wrong with having it indoors, in the lab?"

"Because it has to be mobile, of course," the professor said sharply. "It's no use having it here, is it?"

"Isn't it?"

"Of course not! How could you possibly expect it to work here?" The professor waved his arms around, encompassing the car park, the Department of Sciences, the campus itself.

"It does work, though?"

"Why do you ask?" Professor Anstruther narrowed his eyes. "You have a need to travel through time?"

"That's why I'm here. I told you, I'm writing a paper on the retrospective socio-historic impact of revised quasi-minor pre-contemporaneous events."

"The what?"

"The effect of simple decisions on subsequent history. If the internal combustion engine or the atomic bomb hadn't worked, if Hitler's mother had a headache..."

"A headache?" The professor looked confused.

Sue rolled her eyes. "Never mind. I really would find it ever so useful to be able to study such phenomena at first hand."

"You wouldn't be allowed to change anything. That's the primary rule of personal time displacement technology. If you went back to 1939 and..."

"I appreciate that, Professor. All I want is to be an observer, to spend a brief time at a number of critical periods in history. We can speculate until we're blue in the face, but none of us was there to tell what it was really like."

The professor seemed to make a decision. "Come inside," he said, producing a bundle of keys on a chain and thrusting one into a padlock attached to the side door of the white van. The door swung open silently. "I'll go up first and put the lights on." He clattered up the metal steps and opened an inner door.

Sue followed him. The van was surprisingly warm inside.

"We leave the heating on full time to keep the equipment at a constant temperature. When the engine is running, it powers all the systems. You're not interested in the mechanical aspects, the electronics... ?" It was phrased as a question, but it was a statement. "Silent generator up the front, sound insulation, computer system in the cabinet on the left, extra-high frequency radio equipment on the right. We generate a field approximately two point three metres wide, extending one point nine metres outwards from the back of the lorry. The subject will have to stand in this field to be transported. We've more or less wholly eliminated problems with the temporal-spacial displacement factor due to shift in the earth's magnetic field over a period of time; and the initial difficulties with time control, i.e. the control over the actual number of years, days, seconds that the subject is displaced is now pretty well sorted out." Sue carefully unglazed her eyes and nodded. The professor was one of those people who actually said i.e. in the middle of a sentence.

"So in other words, it's all working perfectly?"

"More or less, yes."

Which was what Sue thought. There were a few too many 'more or lesses' and 'pretty wells' in the professor's description, but he seemed pretty well confident of the time machine's capabilities. More or less. "How long would I have to wait for my turn?"

"Your ... turn?"

"How long before I could make a trip? I suppose the machine is fairly well occupied most of the time?"

Professor Anstruther collected himself with an effort. "Er ... there would be a slight delay before we could accept your booking, but only a few days. You mean you do want to travel?"

"Of course!" Sue wasn't as confident as she sounded, but this was the opportunity of a lifetime. "What do I need to do?"

"Leave it with me. I'll run a full systems check tomorrow, then my assistant will need to work on the bugs. Say next Monday evening? It's a full moon."

"A full moon?" Sue looked at him in surprise. "Well, sure. Why not? You mean I can just come along on Monday and tell you where ... I mean, when... I want to go to and you'll, like, dial it in straight away?"

"More or less. Be here at seven." The interview was evidently at an end. Professor Anstruther walked down the middle of the van, turning off lights. He flung open the door. "After you, Miss... ?"

"Susan Bullinger." She clambered awkwardly down the steps on to the ground. It was chilly outside the cosy vehicle, and starting to get dark. The professor was already striding away. "Just a minute!"

He stopped and turned round impatiently. "What is it?"

"Is that it? I just turn up at seven on Monday? Do I need any luggage or anything?"

"Luggage? You're not going anywhere! Whenever you get to when you're going, you will already have an existence, a home of some sort, clothes, pets, a family. You can't change any of it, so if it's not to your taste, that's unfortunate. But it's only for a month. Twenty-eight days, to be precise. More or less."

"A month? But..."

"It has to be. We're using a lunar phase lock. We deliver you at full moon, and we have to collect you at the next full moon, from precisely the same place. We make the necessary adjustments. All you have to do is identify the exact spot, and be there."

"But what if... ?" But Sue was talking to herself.

"Time travel? A time machine? Are you off your head, or what?" Marianne sat on her bed, then rolled on her back, giggling. As she was naked, it was a disturbing sight. Of course, after almost a year, Sue was getting used to having this naked room-mate. These biological types were all a bit weird about their bodies. "Where are you going in this thing, anyway? Or should I say when are you going?"

"On Monday night."

"That's not what I meant. How many years are you going? And in which direction?"

"Backwards, of course. It's in connection with my paper, so I'll have to go backwards. I don't know how far. Maybe to one of the great crossroads of history, that would be fun. To be a spectator at world-forming events. To live in interesting times..."

"It's pretty interesting now," said Marianne, sitting up and reaching for her clean underclothes. "Especially tonight. You sure you don't fancy a double date? I can fix you up with a presentable boy. More or less."

"Not tonight. Thanks all the same. I've got too much to do if I'm going to be away."

"Suit yourself. Hey, Barry's going to flip when I tell him my room-mate's a time-traveller!"

"Don't you dare! Marianne, no! This has got to be absolutely confidential. If word got out that I was travelling in time, there'd be all hell let loose. The Uni would be sending a search party. I'll only be gone for a month."

Marianne sat bolt upright, her breasts spilling unheeded out of her bra to flop on to her round belly. "A month?" She looked up at the calendar, which featured a big-breasted model on a camel. She was wearing only an Arab-style headdress. The camel was naked. "You'll be back for Christmas, at least. Wait a minute! You'll miss the Christmas Ball!"

"Tough! Big deal! I wouldn't have been going anyway. Christmas Balls and I don't agree."

"Shit, Suze! I could have lined up a real dishy male for you this time. Not like last year's. A friend of Barry's. He plays football for the college. Got a lovely bum."

"Thanks, but he doesn't really sound like my type."

Marianne reloaded her bra and looked up. "Suze, don't get me wrong, but ... you haven't had a boyfriend since I've known you. Hardly a date, even. Is it ... I mean, would you... ?"

"I'm not a lesbian, if that's what you're thinking."

"I wasn't. What I meant, is it because of your figure?"

Sue blushed instantly. "What about my figure?"

"Nothing. I mean, you're lovely and slim and everything. Not like my fat arse. It's just ... your bust. Oops! I'm a poet and I didn't..."

"There's nothing wrong with my bust..."

"There's nothing wrong with it, no. You just haven't really got one. Nothing personal or anything. Sue? Suze, come back! I think maybe there's something I can do to help..."

By the time Sue returned to the room, Marianne had gone out, leaving an almost visible haze of musky perfume behind her. There was a brief note scrawled on the mirror in lipstick.

Sorry! My big mouth again...

M

Sue managed a wry grin. Marianne did tend to open her mouth before engaging her brain. It didn't help that she was right. It was no good going out on double dates with her room-mate. Marianne attracted lovers of the fuller female figure. They always swarmed around her, ignoring Sue as if she wasn't there. Even a small-to-average bosom wouldn't make any difference, unless Sue had a pair of real whoppers, the young men would still have eyes only for Marianne. Sue could never have told her friend, but she had once considered borrowing one of her bras and stuffing it. She still woke up, sweating, at the thought of what might have happened if she'd gone ahead and done it.

Maybe, one day, when she had finished with college and had a little cash saved up, she'd see a plastic surgeon. It sounded a drastic solution, but Sue never shrank from drastic solutions. A pair of sizeable breast implants or a trip in a time machine: if the technology existed, why not use it? Drastic plastic.

She turned on the computer and typed a few sentences, then stopped. The words weren't flowing tonight. Coming up on Monday was the greatest adventure anyone had ever undertaken. She couldn't sit and write mundane stuff, not with a trip through time looming ahead of her.

"Which period should I go to?" she thought. "Something really crucial to world history. How about the start of the First World War? In Sarajevo, perhaps?" She stopped. What had Professor Anstruther said? You're not going anywhere. The machine would only transport her back to the right date. She would still be right where the truck had been when she went down the steps. This whole business needed more thought. If she went too far back in time, she might have no way of travelling across country. She might have a carriage and four white horses, or a penny-farthing bicycle. Or she might have nothing. Whenever you get to when you're going, you will already have an existence, a home of some sort, clothes, pets, a family. The words rang in her head. She was at the mercy of the time machine, and was absolutely forbidden to change anything. "I might be one of my ancestors. Or maybe not. In fact, why should I be?" On an impulse she hurried out of the room and down the stairs.

There was a light on in the Temporal Physics Department. She opened the door and went in, her footsteps squeaking on the polished linoleum. "Professor?" No reply, just the ticking of a clock somewhere. She raised her voice above a whisper. "Professor Anstruther?"

A noise in the next room, as if someone had put down a heavy book with a slam. She'd interrupted the great man, and he wouldn't be pleased. He wasn't the sort of man who liked being interru...

"Oh, hi! I thought I heard someone."

It was the face of a young woman, or maybe a girl. Probably one of those women who always looked younger than they really were. She had a friendly expression and she brushed her pale-blonde fringe out of her eyes as she peered around the door.

"I was looking for the Professor..."

"He's gone off home. Left me a shit-load of work. We've got a victim for Monday, apparently." She said 'appearantly' like an American. "Ridiculously short notice, but that's Angus for you. A bull in a china shop. I'm Hayley Wilbraham," she said, remembering her manners and coming all the way into the room, extending a small hand.

"It doesn't matter, I can catch him tomorr..." Sue stopped in mid sentence. Gradually, she was taking in a number of points: the professor's name was Angus, Hayley was his assistant, she had referred to a 'victim' and - what really stopped Sue in her tracks - the girl had a gigantic bust!

Hayley saw the direction of Sue's stare. She could hardly miss it. She put down her hand, then offered it again. This time, Sue spotted the movement and took the hand, blushing.

"Hayley? I'm Sue Bullinger. The professor didn't mention your name. He just talked about his assistant."

Hayley pulled a face. "Shit, he probably doesn't even know I've got a name. He's obsessed with his machine. And my tits, of course! He never looks at my face. He has long, involved conversations with my chest. Who shall I say... hey! You must be the victim? The time traveller?"

"Victim? He's booked me for Monday. I assumed the machine was fairly busy."

"Busy? It's never been used! You'll be the first. We've just got this year's funds and I've been able to rewrite some of the routines. Angus is brilliant, but I'm the one who has to do all the coding. And making the coffee. You want a cup, or would you prefer tea? We can have a cup and talk while I'm entering data. Come on, Sue, it gets lonely in here at night and I've still got another two hours to go."

Hayley had already turned to go back into her other room, leaving Sue no choice but to follow. She was childlike in stature, but her bosom was clearly visible from behind, swelling out on both sides of her slender torso. She filled the kettle. "Ah, no choice, I'm afraid. We're out of tea bags. It's instant coffee or instant coffee. Black or white. What were you going to ask Angus, anyway? Maybe I can help?"

Sue had almost forgotten. Other, more important questions had arisen. "It was really, like, my identity when I get to the past. I mean, who will I be?"

Hayley stared up at her, stirring a mug. "Yourself, of course. Who else could you be?"

"I mean, how can I be me if I go back to before I was born?"

"That's a problem, yes." She handed Sue a mug and sat down on a swivel chair in front of a computer monitor. "But it's simple enough. You're you as long as you go back to some time when you actually existed. Assume you go back to last year. You'll be who you were last year, doing the same things, except you'll be a little bit aware that you've already been through this once and you'll know what's going to happen. More or less. Of course, you mustn't change anything. You just observe. If you want to, you can change your actions in the present when you get back, because you've had two looks at the past and you get a different perspective on things. Okay?"

"Not really."

"It's all right, it takes a bit of explaining. Excuse me if I carry on working." She took a swig of coffee, put on an enormous pair of glasses and started hammering figures into the computer at lightning speed. She had to sit slightly sideways on, working around her breasts. Rows of data started scrolling down the screen as she typed. "Say you went back to when you were a baby, you'd be a baby and you'd think like one. You might know you had been there before, but it wouldn't be any help because a baby doesn't have the experience to recognise such abstract concepts as having been a baby twice. You couldn't explain to your mother that you'd been there before." She adjusted her position. "Sorry about this. I have to keep changing sides when I'm typing."

"It must be difficult..."

"Can't do anything about it. I can't change anything, can I? I've got giant tits, and that's it. They have their compensations..." She typed a furious burst, to make up for lost time. "Besides, the problem isn't the tits, it's the keyboard."

"How old are you?"

"Me?" Hayley looked at her curiously. "Nineteen. Yes, I know! I only look about twelve. I've got rather a high IQ, I suppose. My brain supports multi-tasking. Extremely busty blondes have an unfortunate image. I'm here to tell you none of it is true! Don't let your coffee get cold. Where was I?" The typing went on uninterrupted. "Right, if you went back to before you were born, you'd assume another identity. That can be fun, especially as you're only there for a month."

"Yes, but whose identity is it?"

"Yours, of course." Hayley turned her body again, joined her hands behind her head and performed a series of shoulder movements which caused enormous upheavals beneath her T-shirt. "You'd be the same age as you are now. It doesn't seem particularly logical, but it's just the way it works."

"I wouldn't automatically have the same family, then?"

"Not if you went back to before you were born."

This put a different slant on things. She'd have little or no idea of what kind of lifestyle awaited her in the past. She would be herself, but she could be anyone.

"You want my advice?"

"Yes, please."

"Don't go too far on your first trip."

"You mean, it might not work? The machine?"

"Of course it will work!" Hayley revolved her chair and regarded Sue solemnly, her breasts rebounding. Sue wanted to ask if she was wearing a bra or not. "I ought to wear a bra," the girl said suddenly. "But I'm going to have to wait a while. I'm still getting fuller. Besides, in a bra, I'd never get near the keyboard! No, on your first trip, restrict yourself to, say, five years back. In fact, it will do one year, or five, then ten. At the moment, we can only do five year intervals."

"But if it's not very accurate, how do I know you'll be here when I come back?"

"It's not a question of accuracy. It's just that the controls don't yet give us fine selection of the number of years. I'd go for five or ten to start with. Later, you can get more adventurous. It's a pain in the butt having to stay a month, but you soon learn to fill the time productively." A frantic volley of typing and the screen cleared, then an image of a family tree appeared. "Come closer," she said. Sue approached, feeling the mass of Hayley's right breast warm against her leg. The girl appeared not to notice. "Here's your family. That's you, just there. There's your mother's line. See? If you went back to just... there ... you'd have a problem. It's okay to die, but not the way your great-grandmother did. That's why the system won't let you become one of your ancestors."

"Oh." She wondered if she dared ask Hayley for a printout of the screen.

"You can have a printout of this. Here you are." She handed over a slim wad of fan-fold paper. "I did it last night."

"Last night? But that was before..."

"Of course! Now, I'd better get on. I can work on three things at once, but the computer can't really keep up. Look, drop by any time. I'm not always as busy as this."

Sue stood up and thanked her for the coffee and everything. Hayley waved happily, then returned to her keyboard.

Marianne tried again on Saturday night. "Come on, Suze! Live a little. Have a little fling before you take off. Barry knows this bloke with..."

"Thanks, but no. I've got to type out a few bits and pieces for my tutor, to cover the next month. As far as he's concerned, I've got to look after my sick mother, but I'll still be working at home."

"O, what a tangled web we weave. Look, you know what I was saying about your figure the other night. You didn't take it personally, did you?"

Sue grinned. Poor Marianne looked so concerned. "Of course not. Believe it or not, I've grown used to being flat-chested by now."

Marianne's face cleared. "Good! 'Cos I've got something here for you to try." She delved in her purse and produced a small plastic cylinder with a screw cap."

"Something to try? What's that?" Without realising it, Sue found herself looking at the cylinder in her hand. It felt curiously heavy, full of liquid of some sort. The label was unhelpful. It simply said:

Sample Number 13

"What is it?"

"Just a little hormonal treatment. You drink it. Not all at once. You have to take one third of it each day after meals from the time your period starts."

"It wouldn't work for me, then. I only have one meal a day."

"I don't think it's the meals that matter so much as the timing. If you came on first thing in the morning, you'd take a dose then. Then another at lunchtime and the rest of it in the evening."

"And then what? Tell everybody to stand clear?"

"More or less! It's true! We've tested it, and it works. I'd have told you earlier, only we've been testing."

Sue shook the container. The contents moved sludgily. "How do you test something like this? On rats?"

"The real answer is we can't, of course. It would take years to get permission. That's why we've taken a short cut. We tested it on three volunteers. And would you believe it? One hundred per cent success! More or less, anyway."

"What do you mean?" Despite herself, Sue was fascinated. "You've got three patients with instant boobies?"

"More or less instant. It takes a week or so to start working. About a month before the results really show. And here are the results. Ta-da!" Marianne produced an envelope, one of those folders from a photo processor. She took out a small stack of pictures and thumbed through them. "Here you go, look. Vicki, Lyn and Diane. These are before..." She handed them over.

Sue studied the pictures. There were two of each girl, a front view and one from the side. "You certainly chose three different types."

"We had no choice, really. These were the only ones who volunteered. Now it works, we've got more volunteers than we can handle. You're lucky I saved a dose for you."

"Hey, wait a minute! Who said I wanted any?"

"Of course you do! You want to look like this, don't you? This is Vicki. After!"

It was impressive enough. Vicki was tall and slim and had been almost completely flat-chested. In the two pictures taken after the event, her shirt was comfortably filled with a pair of what looked like grapefruit. "So she's got grapefruit up her shirt!"