'Here, give me a hand with this.' The Doctor was wrenching the piece of plywood away from the window. With her help, it came away easily, revealing the street-lamp glow from just below and a surprising amount of starshine from above.

The Doctor fished in one of his coat pockets and removed a huge ball of string. He turned it over and over, looking for the end. His hands were large, his fingers were long and slender. She found herself watching them in fascination as heteased out the end of the string. 'Now,' he said. 'We're going to rig up a little surprise for Eva. I'll need your help.'

'What do I do?''For a start,' he said, 'hold that cupboard door open.'

He attached the string to the inside doorknob, and walked backwards, carefully, towards the closet. He tied something inside, and then went to the kitchen, continuing to unwind the string.

OK. 'So what do you do when you're not hunting vampires?' she asked.

He shrugged. 'Whatever I want.' He looped one bit of the string around another. 'I can go anywhere, do anything, with anyone I want to.'

'What I wouldn't give for a life like yours.' Might as well start trying to broach the subject... 'And you just pick up people like Sam and have them travel with you?'

He nodded, intent on his work. 'I can always use another pair of hands. Would you hold this for a moment?'

Carolyn took the ball of string and stood there with her heart in her mouth, wondering if that was an offer. If it was, it certainly sounded like a better deal than the endless grind of classes and lab work and exams. Running off with a tall, dark, handsome, mysterious stranger and a young femme fatale – two for the price of one. Hey, she wasn't picky: she'd take either.

The Doctor had got a knife from the kitchen. He took the string from her, sliced through the strong stuff, and tied off the end. 'All right then, I do believe that's taken care of it.' By now the whole apartment was filled with string, crisscrossing around the ceiling in crazy patterns, tied to everything. The Doctor ran a critical eye over it, adjusting a knot here, moving a line of string an inch to the left here.

He was slowing down as she watched, all the mad energy disappearing back to wherever it came from. He beamed at Carolyn for a moment, then took a couple of steps towards the window and sprawled out in Eva's beanbag chair. He was just as completely relaxed as he'd been completely focused a moment ago.

He hadn't opened the door by magic, she suddenly realised. He'd picked it when they weren't looking. Sleight of hand. Show-off. 'I still don't believe you're a spaceman,' she said.

'Carotid pulse,' he said idly.

She knelt down next to the beanbag. 'Go on,' he said. She reached out and pressed her fingers against his throat, gently.

He watched her, clear eyes in the dim light, his hair in disarray around his long face. She caught a faint scent, like sandal-wood incense.

She felt her own eyes go wide as she felt the four-four time of his pulse under her fingertips. There was no way he could fake that.

'OK,' she said. 'So where are you from? Mars?'

'Much further away. A world you've never heard of. Gallifrey. But as the song puts it, I've been everywhere.'

He jumped up, and inched the plywood away from the window. The strings moved, and he gingerly pushed it away from the glass. The excitement was there all over again as he pointed out of the window.

'See that one?' he asked, tapping his finger on the glass. 'The red star, just to the right of the building across the street.'Carolyn looked, hoping she had the right one.

'On the fourth planet out from that star, there's a race of intelligent sea serpents who worship whales as gods. The whales on that planet aren't intelligent, of course, and the serpents know that, but they believe the whales are so enlightened that they don't need to be intelligent. Around that one' – he pointed again – 'there's a frozen world where an old enemy once stranded me. I had to build a fire to keep warm till I could be rescued, and I ended up throwing one of my favourite ties on the fire to keep it going. And around that sun' – he pointed at another star, directly overhead – 'there's an ice-cream shop where they kept me waiting an hour and a half for a chocolate milk shake. Can you believe it!'

Carolyn burst out laughing. 'No way.'

His eyes were utterly earnest. 'I mean it. The shop was mobbed. I tried to complain, but the man behind the counter was just swamped. "I've only got six hands!"he said...'

It suddenly occurred to her that she believed every word of it. Little green men had always seemed ludicrous, but somehow little green men serving milk shakes had a kind of a ring of truth to it.

Of course it made no sense, but the possibilities of how interesting nonsense could be were unfolding before her eyes.

She looked out of the window. 'This is what the sky had looked like when I was a kid,' she said.

'So,' asked the Doctor, 'what do you do?'

They'd been waiting for an hour. The Doctor was sitting on the floor, back against the wall, while she dozed in the bean-bag. She'd heard him go out, speaking with Sam, low voices at the edge of her consciousness. When he'd got back, she was wide awake.

'Not much,' she said. 'Nothing that compares to fighting Daleks and stuff like that.'

'Oh, tell me anyway,' he said. 'I know all my stories – I'd rather hear yours.'

'All right... I'm a student. Undergrad at UCSF, majoring in biochem.'

'What for?'

'What?'

'Why do you want to learn that?'

Now she could see where Sam got it from. 'Well, I'm kind of interested in cancer research,' she hedged. 'Not that I get totake any classes about it – they don't teach you any of the good stuff until they've spent a few years boring you with things that'll probably be irrelevant to whatever you go into anyway.'

'Oh,' he said, 'so you study it for fun then.'

'Hardly,' she snorted. 'Well, I suppose it's sort of a hobby, if you can call it that. I want to go into the theatre. Sad, isn't it? What a life.'

It was odd: he didn't nod or anything, he just kept acting interested. 'Tell me more about it. What have you found out lately?'

'Well, I haven't crashed any flitters on Mars recently.' No way will he ever want to have me run off with him and Sam now. 'I'm doing this research project on a new test for environmental carcinogens, using frame-shift mutations... I'm sorry, I'm boring you already.'

He waved that away. 'No, no, go on, it sounds fascinating!'

'Well, they just developed it. It's based on the principle that mutagens are also carcinogens.' He nodded enthusiastically. 'You start with a mutant strain of Salmonella that can't produce histidine, expose them to the chemical, and see if anycolonies revert to wild type...' With a shock Carolyn realised he really was fascinated, his eyes as wide as a child's, being told a fairy story.

She laughed in disbelief. 'It's not that fascinating to me.'

'Oh? Why not?'

'I don't know.' After all, wasn't this what she wanted to do with her life?

He leaned forward and grasped her hand. His face was so alight she figured she could read by it. 'It always amazes me how everything fits together,' he said. 'All the patterns that people would never suspect are there just to look at them. The way that atoms make up a molecule, molecules make up a protein, proteins make up a cell, cells make up people, people make up worlds. The tiniest interactions of these obscure little unrelated parts can change everything on levels you'd never dream of.'

She nodded. 'Yeah. A tiny change in a person's genes, and they get cancer. Or blue eyes.'

'It's stunning, it's something I could never come up with in a million years.' He grinned suddenly. 'Why not get enthusi-astic about it?'

'I dunno,' she said. 'You just don't get overjoyed about things like lipids.'

'A pharmacist on Lacaille 8760 once gave me a half-hour lecture about lipids. Did you know that if you suddenly lost all of your lipids, your cell membranes would disintegrate, and your whole body would melt into a puddle? Think about that –isn't it just bizarre?'

'Guess so,' she said, feeling the beginning of a smile. She hadn't thought about things like that for a long time.

'Go on. Please,' he asked.

And she realised, as she rambled on about the Ames test and base-pair substitution, that she really could remember feeling the way he did about it. It had taken high school and college to drum that enthusiasm out of her, to convince her it was a chore, obscure and anally retentive and dull.

She really was allowed to enjoy it. She'd forgotten what that felt like.

She found herself staring at his elven face with something close to awe. So what if maybe he'd picked the apartment lock before she'd got to look at it? So what if his saving her from Eva had been all bluster and psychology? That didn't changethe effect he had on the world around him.

He was magic