Sarah Jane lived just across the square from Carlucci's, in the last of a long row of tall, grand Georgian townhouses, the sort that looked like they had been faced with royal icing. Even though this was a very central area, within a few minutes' walk of London's major shopping streets, the square wasn't a through-route for traffic and consequently, was as peaceful as a leafy village. Sarah led her through a flagstone hallway with a magnificent staircase curving upwards, and down a smaller flight of stairs at the end of a corridor to a huge, light-filled kitchen. It was, seriously, the nicest house Rose had ever been inside. On Earth, anyway.

There was a teenage girl sitting at the kitchen's wooden table, with what looked like schoolwork spread in front of her. She had the long, straight, shiny hair typical of posh girls, and was wearing a loosely-knotted striped tie and v-neck school jumper. "Shall I go?" she asked, with a quick glance at Rose, gathering her books together as she spoke.

"If you don't mind, Tamsin."

"No problem. Ginny and Arabella are coming round at eight, is that OK?"

"Sounds like a fait accompli."

"Thanks, Mum. We'll be quiet."

"My younger daughter Tamsin," said Sarah, once the girl had clopped up the stairs with her books. "She's used to strange people coming here at odd times. She knows to clear the coast."

"How many kids have you got?" asked Rose, with a strange feeling. The 'real' Sarah Jane – or at least, the Sarah Jane of her own reality – was childless.

"Three. The other two are a bit older. Lavinia's at university and Matthew's working for a charity in Afghanistan."

Rose nodded.

Sarah had been fiddling with a complicated coffee machine onone of the kitchen's many marble-topped work surfaces, but she left it to hiss and pulled up a chair at the table. She was shining with some kind of barely-contained emotion. "Tell me everything, from the start."

"Well – that's difficult, cos it's going to sound like I'm completely off my rocker, if I do."

"I'm used to hearing some fairly outlandish stories – Rose, isn't it? Just try me. Tell me a bit about yourself, to begin with."

"OK then. I'm nearly twenty-one, I was just living with my mum in East London – the Powell Estate, don't suppose you've heard of it."

Sarah Jane shook her head.

"It's a long way from here. Don't get me wrong, it's not a sink estate or anything, it's not that bad, but – well, compared to here, I mean."

"I understand."

"Two years ago, I was working in a shop in the West End – Henricks, you probably have heard of that. And I met a man called the Doctor. Just that, no other name. He was a traveller. OK. He turned out to be an alien. From another planet alien, I mean. He looked human, but he wasn't. He had two hearts, for a start." She had been talking to the table once she'd got to the alien bit, but now she risked glancing up at Sarah jane to see how she was taking this. She was looking amazed again, eager, as if she were still reigning in that anxious delight. "You do know him, don't you. You know what I'm talking about."

"For years," said Sarah Jane, "I've had dreams. Probably starting from when I was around your age, I've had very vivid dreams, about a man called the Doctor – not a man, but an alien, with two hearts. And he takes me into a large blue box…."

"That's the TARDIS."

"Tell me what happens once you get inside."

"It's bigger. Much bigger on the inside than the outside."

"A huge, beautiful spaceship – a time ship?"

"Yes," said Rose.

"And you step straight into a control room with a huge, central column that rises up and down when the ship's in flight – and circles set into the walls, everywhere." Sarah Jane's face was radiant – then she broke off, put her hand to her mouth, and looked aside with tears glistening in her eyes. "I've never told anyone," she said, after a moment. "Let alone written about it. Not my husband, not anyone. Yet I've had these dreams every few weeks for years. How could you possibly know?"

"It's OK," said Rose. "To me, these weren't dreams. This really happened, this is happening. But when I woke up this morning, the Doctor had disappeared and no-one remembers anything about him. My mum, my ex-boyfriend, they both knew him really well, but it's as if he never existed."

"Why me, why did you call me?"

"Because the way things should be, what I remember, you used to travel with him like I do now. When you were – when you were my age. And we met, here on Earth, a few months ago. You gave me your number and said to come and find me if I ever needed to."

"Why would you need to?"

"If he ever dumped me, is what you meant, or I left him."

"Ah."

"But here – in this reality – you haven't really met him either, have you. You've just had dreams."

"Very compelling dreams," said Sarah, after a pause. "They've haunted me. It is the most extraordinary thing that you should come here and be able to tell me what happens in them. I don't know what to think about it."

"Well, I don't know what to do. I suppose I was hoping I'd come here and you'd remember too, and be wondering what was going on, same as me. And maybe be able to help put things right."

"How could I do that?"

"I don't know. Something might have happened to you, when you were with the Doctor, that'd help make sense of it. I mean, the Doctor and me, we've been to a parallel universe, where everything is a bit different – like, they have air ships instead of planes, for a start – and there are parallel versions of people, that different things have happened to. Like, my dad died when I was a baby, but in the parallel universe he was still alive, and he'd got rich, and he and my mum were living in this great big mansion. But I'd never been born. She'd given my name to a dog!"

"A dog?"

Rose snorted. "A hairy little Yorkie, you know the sort that look like toilet brushes? But this isn't a parallel universe, because there isn't a double of me. It's like, I don't know, an alternative timeline, what would've happened if the Doctor was never here. You might have come across something like that and know what to do about it. You didn't dream about it, did you?"

Sarah shook her head slowly. "My dreams are vivid pictures of the Doctor – the time ship – terrifying metal monsters called Darlicks? – "

"Yeah, Daleks."

"And for some reason, a robot dog."

"That's K9. You had it with you when we met you."

"None of it makes connected sense. But the dreams are suffused with very strong emotions – wonder – fear…. Can I ask you something personal?"

Guessing what was coming, Rose said, "Yeah, go on."

"This Doctor, is he your lover?"

"He's not really like that. But I suppose that's what it looks like, on the outside."

"Was he mine?"

"I never asked him," Rose muttered. "But I think so, yeah. Oh. The dreams."

Sarah Jane nodded, smiling slightly. "Some, yes."

Rose felt a hot flush work up from her neck to her cheeks, and a rancid surge of jealousy. Well, this was an entirely bizarre conversation. "Before we met up, I didn't know about you," she said rapidly. "Didn't realise that he'd had girls travelling with him before. I thought I was special. But it turned out it wasn't just me, and it wasn't just you. I wondered if maybe the others could help, maybe they'd know something."

"Have you tried to get in touch with any others?"

"No. I don't know anything about them, just that there were some. This seems really stupid now, but I think I was hoping you might know. When we met before, from what you said, you did seem to know that the Doctor'd had other people with him."

"I take it you never asked him."

"No! It's not something you can really talk about with him. He puts people out of his mind if he think he'll never see them again. He has to."

"Why?"

"He lives for hundreds of years. He doesn't age, he can change his body if he's going to die. We just live a few short years as far as he's concerned. I mean, he can't hang onto everyone. He'd go mad."

"Rose… you sound bitter."

"I'm not. I'm just dead worried, and missing him."

"I'm not sure, from what you've just said, that he's worth it."

"You told me that some things are worth getting your heart broken for."

"I did? That doesn't sound like me at all."

"Well, the Doctor does that to people. He changes them."

"For the better?"

"Yeah! Look at me. My life was going nowhere at all. I was living with my mum in a council flat, I was working in a shop, I had a boyfriend who was nice but looking back, so unexciting. I never got any qualifications, left school with two GCSEs. What future did I have?"

"All your future. You were nineteen! You could have done anything with your life."

"Easy for you to say, sitting here with all this."

"But nobody came along and gave me all this, Rose. My parents were teachers, they still live in a very ordinary semi in South Croydon. I've worked hard all my life and taken chances."

"Well, you're famous, aren't you."

"That didn't happen overnight. I had some lucky breaks, yes, but I had to create the opportunities myself. The house isn't just down to me, anyway, Derek – my husband – a lot of what's gone into it is his hard work too."

"Yeah, sorry."

"All I'm trying to say is – and look, I don't want to some patronising, but I'm probably older than your mother – you're very young. You can make your own life."

A terrible feeling of desolation swept over Rose. She looked around at the kitchen, all flagstones and maple, marble and chrome, spotlights and infused oils in dark, sleek bottles. And she looked at Sarah Jane, so beautiful and poised, so full of confidence, sympathy and charm. Was this actually where she would have been without the Doctor?

Like Clive Finch would be still alive and hosting nutty web sites, and Elton Pope would be playing in amateur bands with his unpetrified girlfriends. The only thing she seemed to have done with her Doctor-free life was dump Mickey, which didn't seem like that great an idea anyway.

"Don't look so downhearted," said Sarah. "I understand, I do. The flashes I've had of the Doctor in my dreams have been very intense, very compelling. But I thought he was just someone I'd imagined. Real men like that can be dangerous. I have met one or two, and they wreck lives. You're about the same age as my elder daughter, and if she was getting into a relationship like that, I'd try to warn her against it. She wouldn't listen, but I'd try." She smiled.

"It's not a question of whether I listen, though, is it. He's gone anyway."

"Do you think – is this possible – " Sarah tilted her head back, considering. "Could he have caused this to happen, in some way? Deliberately, I mean?"

Rose shook her head violently. "No."

"But what if he'd thought about it, and decided that perhaps you were better off without him. Maybe… I wonder… is it at all possible that I had my memory erased, but imperfectly, so that the memories have come through as dreams ever since? Maybe I did really travel with him, all those years ago. And he took you back home and wiped your memory, too, and your family's, but for some reason, with you, it didn't work at all."

"No!"

"It's a suggestion," she said gently.

"No, because in my world, if it is another world, you're different."

"Different?"

"You're not married, you never had kids, you're not famous and on the telly and everything – "

"Oh!" Sarah Jane's eyes widened. "What am I doing with myself then, in this other version of events?"

Rose bit the inside of her mouth. She hadn't actually meant to tell Sarah Jane any of this, but she'd been goaded into it. Anyway, if she was going to get any help, she had to describe the whole situation. "You're still a journalist, but you write for newspapers and things, and I'd never heard of you like everyone has here. And all I know is, you never married and you don't have kids."

"Tell me I didn't spend my life pining away for the Doctor."

"Uh. I think you did actually."

Sarah was silent for a while, and a hard faraway look came onto her face, and she tapped on the wooden table rapidly with her teaspoon. "For years I've thought about the dreams," she said eventually. "Longed for the fantastic worlds I kept glimpsing, longed for the man, longed to experience for real the kind of love I felt for him while the dream lasted. But it's not real, you know. It can't be real. It can't make for a happy life."

"I am happy! Or I was, til this happened."

"I'm glad," said Sarah, "that none of this really happened to me."

"But what am I going to do? I need to get back."

"Maybe you should leave things as they are, and get on with your life."

"I can't."

"All right, but I don't know what to suggest! The dreams are all I have."

"I had a dream too," said Rose suddenly. "This morning, before I woke up to all this. I dreamt the Doctor was calling my name, over and over, in my head – as if he was far away and he couldn't get to me, but he was trying to reach me."

"Maybe that has some significance. Did it feel lucid – very intense?"

"Yeah, very."

"What if you go to sleep again, and see what happens. Maybe you'll learn something about what's going on if you have another dream. Maybe the Doctor is trying to reach you!"

"You haven't had any different dreams like in the last couple of days?"

"No. But about a week ago I had a very peculiar one. The Doctor was standing in front of me, but he looked different. Completely different, I mean – another man. But in the dream, I knew it was the Doctor all the same, and I seemed to remember a time when he'd been different before. Does that make any sense?"

"Yeah. Loads of sense, you don't have to tell me."

"He was young, dark haired, had a slender face, pretty-boy looks – but with burning eyes. He took my hands, and pressed them, and I had a poignant sense of loss and sorrow. I woke up with tears in my eyes." She shook her head. "Maybe he's trying to contact me, too."

"Yeah, maybe," said Rose, ashamed to feel another twist of jealousy in her gut.

"Look, maybe this is an insane idea, but it's all I can think to suggest. Why don't you spend the night here, and perhaps we'll both have dreams that could tell us something."

"You're not worried I might nick your candlesticks, or something?"

"I'm a good judge of character. I have to be. And I work on intuition, and something is telling me that we ought to stick together."

Rose had some difficulty persuading her mum not to create merry hell when she phoned to say that she was spending the night with a friend.

"What about the baby? What if something's wrong?"

"Mum, there's nothing we can do about it until the appointment next week. What do you want me to do anyway, stay at home every night for the next six months?"

"It'd keep you out of trouble!"

Sarah Jane showed her into a room with vast high ceilings, pale embossed wallpaper, oak floorboards overlaid with antique rugs, and a bed spread with cream and chocolate, silk and faux fur. Through the window, which was taller than a man, Rose could see across the trees into the enclosed private garden of the square below.

"Bathroom's through here." Sarah opened an interior door to a glimpse of chrome and glass and deep azure tiles. "It was a dressing room, we did a lot of work on the house when we bought it – it was in a terrible state, been lived in by an old theatrical dame for fifty years. Which meant that the features were all there – " She tapped the marble fireplace - "but there was one bathroom for the whole house, in the basement!"

"It's lovely," said Rose, distracted.

"Well," said Sarah Jane, pausing awkwardly at the door. "Sleep well. Let me know if anything happens. If there's a problem, we're just upstairs."

"Thanks."

She tested the bed, which looked like something from an interiors magazine that really not ought to be disturbed. The pillow smelled of perfume, not fabric conditioner. Sarah Jane had leant her a nightdress, which turned out to be tight around her hips. She wasn't exactly the same shape.

So, all she had to do was sleep and dream. She was never going to manage that.

She realised that it felt more like home that home, to be somewhere odd. With the Doctor, you just never knew where you might end up sleeping next. This wasn't the most luxurious place she had ever lain her head, that would have to have been the Palace of a Thousand Stars on Querota where the Emperor had received the Doctor and her as honoured guests. True, they'd tried to marry the Doctor the next morning to the Crown Princess and they'd had to make a pretty smart getaway, but while the going was good they'd enjoyed the silk-draped bed, mounted on a plinth and surrounded by an ornamental moat. Oh yes.

She curled round a pillow, hugging it for comfort, breathing scent. She could never sleep.

She shot upright, filled with terrible and instant panic.

There was a shape in the dark, moving black against black.

"Shit," said a man's voice, a stranger's but faintly familiar. Then, "Don't scream. Don't make a sound. Don't move – "

She scrabbled to find a bedside light, and a hand clamped over her wrist hard enough to hurt.

She smelled a wave of spicy aftershave, and felt a cold spot on her neck, and then nothing.