'Bye Jack,' she called. 'See you later.'

'Bye.' He didn't look up. The meerkats were more interesting. The babysitter was relieved no tantrums to deal with. Good.

As Kate opened the door to leave, the babysitter sneezed.

Kate turned back. 'Have you got a cold?'

She shook her hood. 'Maybe I am getting one.' It was just a tickle.

'Hmm. Well, it depends if your body has encountered this virus before. If so, your antibodies will fight off the cold and it'll go away.'

The babysitter nodded, not knowing what to say. She was pleased when the anxious mother finally left.

Kate emerged from the tube station and checked her watch. As so often happened, she had rushed out in a hurry and arrived early. Vernon was always going on about her obsessive need to be punctual and reliable. In the early days, he found it endearing, a positive character trait. Later, it became another sign of her uptightness.

She walked up Charing Cross Road and stopped outside a bookshop full of medical and scientific books. She recognised some of them. There was a famous book called The Plague on the Horizon, which contained several quotes from Kate. She had a signed copy back in Boston. The author had interviewed Kate because of her involvement into the investigation of the West Nile Virus, a potentially lethal illness that had first been seen in the US, in New York, in 1999. WNV, as virologists called it, caused muscle weakness and confusion in some people, and could lead to meningitis, paralysis and death in others. It was a particularly interesting virus (and when Kate said this to non-scientists they would raise their eyebrows, wondering how anyone could find such a horrible thing so interesting) because of the way it was transmitted. Mosquitoes became infected after feeding on virus-carrying birds, such as crows. That mosquito could then infect a human. Kate's team were trying to develop a vaccine for WNV. So far, they had not been successful.

She caught sight of her reflection in the dark gla.s.s. She was pale, her eyes wide. She hadn't been able to decide whether or not to wear make-up. This certainly wasn't a date, but sometimes make-up made her feel more confident, less exposed to the world, so she'd put on a slick of lipgloss, a touch of mascara. Still, she wasn't looking her best. A large part of her wanted to be locked up safely behind the door of her hotel room with the TV on and Jack beside her. She hoped he'd be okay. That babysitter had seemed capable enough, but she let her imagination reach out what if she was a child-killer, a front for an international child-slave racket, or just plain irresponsible?

She castigated herself. Don't be ridiculous, Kate. Relax. It's a reputable chain hotel, the woman had references.

She pushed her hair behind her ears and stood up straight. All you're doing, she reminded herself, is meeting the brother of an old boyfriend.

His name was Paul.

'We were twins,' he had said, a second after telling her he was Stephen's brother. Stephen had never told her he had a twin, which seemed very odd in retrospect.. Maybe probably he did tell her, but she'd forgotten. So much of that summer was obscured behind thick fog. When she tried to remember those days, it was like trying to read a road sign without her contacts in. No matter how hard she strained, she couldn't make out the details through the haze and, in the end, the effort became painful and she gave up.

When she replayed in her mind the ensuing minute, it made her cringe. She had felt so awkward, and Paul seemed uneasy too. Being followed does that to you. So must being confronted by a woman who is staring at you like you're a phantom.

He told her his name and said, 'How did you know Stephen?'

Kate had been aware of Jack looking up at her. Part of her wanted to turn and run. But she was hypnotised by the face of this stranger who looked so much like the man she'd loved long ago. Alongside unease, his face showed kindness, just as Stephen's had. She had the sudden urge to launch herself at him, wrap her arms around him and kiss him. For years she had dreamt of a moment like this of b.u.mping into Stephen and him telling her, 'It was all a mistake. Reports of my demise were exaggerated.' And they'd embrace, and the years would disappear.

Except this wasn't Stephen.

'We were friends,' she said.

'At university?'

She almost told a second lie, but said, 'No. I met him at the Cold Research Unit in Salisbury.'

'Oh.'

She said, 'I was there.'

He spoke softly. 'There...when he...?'

'Yes.'

Jack had spoken up then. 'Mummy, what are you talking about? Billy's bored. And he needs to pee.'

Jack's words broke the tension and the adults laughed.

Kate said, 'Look, I'm really sorry. I don't normally follow strangers through the streets.'

Paul smiled. 'It's okay. It's understandable.'

'Maybe. But I'd better go and get Billy and his master back to the hotel.'

'Hotel? You don't live in London?'

'We live in Boston,' said Jack.

'Really?'

Kate went to turn away, but hesitated. She didn't want to say goodbye to this face, but lingering there was pointless.

Paul said, 'Wait,' even though she hadn't yet moved.

'Would you like to meet for dinner?'

'I...'

'It would be nice to talk to someone who knew my brother. Our parents won't talk about him because it's too upsetting. I never see any of our old friends these days. Sometimes it feels like he never existed.' He smiled wryly. 'Except I see him every time I look in the mirror.'

Kate didn't know what to say.

'So, dinner? You can bring Jack and Billy, is it? if you like.'

Before she could change her mind, she blurted, 'Where? What time?'

He pointed up the street at a restaurant. 'Do you like Chinese? We could meet there at seven.'

'Alright.' She turned away, then realised she hadn't told him her own name.

'I'm Kate,' she said.

Something happened when she said that; it was as if the name meant something to him but he wasn't sure what. The moment pa.s.sed and he smiled. 'Okay, I'll see you later.'

She killed twenty minutes walking slowly through Soho towards the Chinese restaurant. It was a warm, overcast evening, and the streets were rammed with people in T-shirts standing outside pubs. She hadn't smoked for years, but she had a craving for cigarettes. And cider. She thought she knew why, too: she was going to meet a man she didn't know for dinner, something she hadn't done for a long, long time. It threw her back in time, made her feel like a teenager. She wouldn't smoke or drink cider, or go to bed with this man, but she wouldn't be enormously surprised with herself if she did. She'd done enough out-of-character things recently.

She paused outside the restaurant, inhaled the smell of cooking rice and sweet and sour sauce and MSG. She watched a trio of chickens rotating on a spit in a window opposite and had to look away. She hadn't eaten meat, either, for years. Another thing that irritated Vernon living with a G.o.dd.a.m.n vegetarian.

'You enjoyed the taste of meat when we met,' he said, the underlying innuendo making her shudder. She had to stop thinking about him. But how could she? When he found out what she'd done, as he would very soon... She didn't want to think about it.

She didn't have to. Paul arrived at that moment, appearing out of nowhere and grinning nervously at her.

'I left Jack with a babysitter at the hotel,' she said. 'I hope he's OK. I just thought it would be easier to talk without interruption.'

'Sure,' he said, easily.

She'd been worried that he might think she was planning to come on to him, farming her son out to a stranger, being a bad mother but he didn't seem at all phased. 'I'm starving,' he added.

'Me too,' she said. A white lie.

He led the way into the hot, noisy restaurant, waves of chatter rising and falling amid the clank and clink of cutlery, and a waiter showed them to a table, chucking a pair of menus down on the table and zooming away.

Seeing how taken aback Kate was, Paul said, 'They're famously rude in here. It's part of the appeal.'

They exchanged pleasantries about the warm weather and Chinese food for a few minutes, ordered drinks and studied their menus. The waiter reappeared and brusquely said, 'Yes?'

Paul gave the waiter a few numbers from the menu, and Kate did the same.

'You're vegetarian?' he asked. When she nodded, he asked, 'Do you eat fish?'

'No, I'm vegetarian.' She immediately regretted her snappiness. 'Sorry, it's just that everyone always says that it's like an automatic response. Proper veggies don't eat fish.'

'I'll remember that.' He pretended to make a note on an invisible notepad. 'Fish have feelings too.'

He was charming. Just like Stephen or rather, how Stephen would be if he'd had sixteen more years to practice. She had to keep reminding herself, though, that this wasn't Stephen. She had to remember that she had only met this man this afternoon. Her fantasies were not coming true. On the way over, she kept asking herself why she was doing this, what her motives were. There were, in the end, two things.

One, she had never been able to talk to anyone else about Stephen. Now, like his brother, she relished the chance to talk to somebody about him, somebody who knew him intimately. Perhaps that way, after all these years, she could achieve some kind of and she hated the word but couldn't think of a better one closure.

Two, she was glad of the distraction. She had only been able to think about one thing since arriving in London. Her brain needed a break from the worry. What better way to stop fretting about the future than to concentrate on the past?

'So,' Paul asked. 'What brings you to London? Visiting relatives?'

It was far too complicated to explain, even if she'd wanted to. 'No. Well, not really. Jack and I are just about to move over here.' She played with her chopsticks, unsure of how much to tell him. 'I'm looking for a place at the moment. Actually, I'm kind of shocked by the price of property in London.'

'Where do you live at the moment? oh yes, you said earlier, didn't you: Boston, wasn't it?'

'Yes.'

'Nice.' He waited for her to give more details but she wasn't forthcoming. 'And what do you do in Boston?'

'I work at Harvard.'

'Doing..?'

Kate laid her chopsticks on the table. 'I'm a professor in the department of immunology and infectious diseases. I specialise in the study and treatment of viruses.'

She watched Paul closely to see his reaction. Telling people what she did usually had two effects. Weak men, the kind who were intimidated by clever women, would try to outsmart or belittle her. Other people would inch away, like people she talked to on the extremely rare occasions she went to parties, as if they might catch something from her.

Paul didn't appear to be at all intimidated or frightened. 'Cool. So is that how you knew Stephen? You worked with him at the Cold Research Unit?'

'No, I was a volunteer there. I'd only just graduated. And after that, I went to Harvard and, apart from the odd visit, never came back.'

'Until now?'

'Until now,' she echoed, thinking how strange it was that you could summarise a life so quickly and painlessly. Only the details were missing. Of how she went to Harvard, still in a state of shock, only weeks after Stephen's death. The years she spent in the graduate research programme. The glorious day she became Professor Kate Carling. Meeting and marrying Vernon Maddox and having Jack. The happy years, and the deterioration.

She could sit here and talk all night, adding layer after layer of detail to those basic facts, like peeling an onion in reverse. And after that, Paul would know her story. But he would still only understand a fraction of who she was.

'And what do you do?' she asked.

'You might not believe this, but I chase viruses too.'

'Really?'

'Yes but a different kind to you. Computer viruses. Or I should say, the sc.u.m who create them and send them out across the internet.'

'You're a cop?'

'No. Not really. I work for an internet security firm. It's a very exciting business.'

She smiled. 'Sounds a bit geeky to me.'

'Er, says the professor of what was it? immunology and infectious diseases?'

'Touche.'

Paul laughed. 'Actually, a lot of people think it's a geeky job, and I do spend a lot of time staring at computer screens. But so must you.'

'You're right. Too much time.'

'Except now you're moving to London. Are you moving to a university over here? Kissing the Ivy League goodbye?'

He asked a lot of questions. Stephen had been curious like that too, interested in others.

Their food arrived, the waiter plonking it down on the table, shoving their gla.s.ses out of the way then stomping off. Kate was too busy trying to decide how honest to be to feel aggrieved by the waiter's rudeness. Should she tell Paul that she had no idea about what she was going to do professionally; furthermore, that she didn't care right now?

She said, 'I'm considering my options at the moment.'

'I see.'

They emptied their beer bottles and Paul put his hand up to order more. Kate licked her lips. She hardly drank at all these days and the beer tasted good: sweet and mood-changing. Tongue-loosening. They talked about Stephen, Paul telling her stories from their childhood, making her laugh until there was an awkward pause in the conversation and she could see him struggling to say something.

'Are you OK?' she asked.

Instead of speaking he reached into his pocket and took out a folded sheet of paper. He didn't show it to her, just held it, gazing into s.p.a.ce. Kate could hear his thoughts ticking away. Stephen used to do this too.

He said, 'As soon as you told me your name was Kate, it rang a bell.'

'Stephen told you about me?'

'Yes. In a manner of speaking. It wasn't something I'd thought about for a long time, but yes, I recognised your name straight away. I went home to check, to make sure I wasn't imagining things, or mis-remembering, and there it was. In black biro.'

'I don't understand.'