To visitors, and there aren't many of those, Matteo says his apartment is a pied-à-terre, that he lives in Milan but that he's in town temporarily for scientific research. For a pied-à-terre, his apartment is nice. It's got rats, but no one notices. At night, when it's quiet, Matteo hears them gnawing. True enough.

Matteo is employed by a science magazine, Nature Methods; four days a week he does administrative work for that magazine. It started off as an after-school job, but after he graduated he never left. He's seen editors come and go, including the editor-in-chief.

When he turned 27, Matteo told everyone he was going to do scientific research. He received his diploma in biology, married more for the green card than for love, divorced eighteen months later, and a woman from the Human Resources department at Nature Methods told him they were very satisfied with his work. He could stay on for as long as he liked. Not as an editor, true, but that would change. Matteo was in possession of an Italian accent, undeniable charm and persuasiveness.

The world lay open, all he had to do was enter.

Now he's 38, and he tells people he's an evolutionary biologist doing scientific research.

He never sees his old friends anymore. For a number of reasons, the most important of which is that they know Matteo isn't doing scientific research. If he does any research at all, it falls under the heading "administrative research."

As soon as his scientific research gets rolling, he'll phone his old friends. The address book with their numbers in it is lying ready on the desk in his little apartment. He knows what he's going to say to them.

Twice a week, on Tuesday afternoons and Friday mornings, he sees a woman. Her name is Shawna.

His charm no longer has its former boyishness, but there's plenty of it left. He found her on the Internet, on Craigslist, in the category "Casual Encounters"—that was two years ago now. A steady relationship seemed like a bad idea to him. Once he got going with his scientific research, he'd start a family. Until then he'd stick to the "casual encounter."

He spent one whole evening scouring the ads in fascination. This, in fact, was scientific research too. He was studying the fantasies of others. But it went no further than studying. Not until one week later, when he resumed his scientific research into the fantasies of others and responded to an ad. The answer was silence.

A few days later, after dinner, he picked up his research again and reacted to yet another ad. Once again, silence was the only reply.

He was actually planning to abandon this research, until one Saturday he responded to forty ads at once. He had been overcome by acute lust, or maybe only the inspiration that has its way with scientists as well. To his brief response he attached a picture of himself.

The picture was five years old, but still current, he felt.

Some of the advertisers had written: "No pictures of sex organs, please. I want to see your face."

Matteo's picture fully lived up to that request.

Three answers came back. One was from Shawna.

They agreed to meet at a Starbuck's not far from Matteo's apartment.

Shawna was small, but not unattractive. Matteo figured she was in her late twenties, maybe mid-twenties.

She had a boyfriend, and that was the way it should stay because he was great, but she had a fantasy, too. And the boyfriend wasn't in it.

"That's how it goes," she said.

Matteo didn't want to be one-upped. "I'm married," he said.

"So where's your wife?" Shawna asked.

"In Italy."

"But why aren't you together?"

"She teaches at a university, I'm here for scientific research."

"But you have a fantasy too, one hopes?" Shawna enquired.

Yes, Matteo had one of those too.

That was enough for Shawna. They went to Matteo's apartment. Fortunately, the day was still young. The noise from the street drowned out the gnawing of the rats.

For the next six weeks or so they saw each other regularly, until Shawna told him she had no more time for casual encounters. She was too busy with her work.

Matteo had never asked what kind of work she did. He had, in keeping with his research, concentrated on Shawna's fantasy.

Her departure was not something he took very personally. It was too bad, he thought, but there were more people with fantasies. Sometimes the city seemed like one big casual encounter, with him as bookkeeper of those transient meetings.

But one Tuesday afternoon that winter Shawna sent him a text message. "In the mood?" she wrote.

In the mood: Matteo hadn't been in the mood for ages. At least, not like before. But seeing as how the halting progress of his own career caused him to avoid other people, he decided to get himself in the mood. A little loneliness, he had always figured, could stimulate his scientific career; too much loneliness, on the other hand, could cause a mental block.

They agreed to meet on Friday morning, Matteo's day off. And then again on Tuesday afternoon, after he came home from work.

And so it went. Week after week. The fantasy had become a ritual and, as with rituals, actually rather comforting.

Until one Tuesday afternoon, as she was putting on her shoes, Shawna said: "Maybe we should try something different?"

"Something different?" Matteo echoed.

Shawna stood up. "Maybe you should come to my place," she said.

She went to the little mirror in the hall, a gift from Matteo's mother, and combed her hair.

"Well?" she asked, "what do you think? We have to come up with something new now and again, otherwise we'll get in a rut."

It mustn't become a rut. The fantasy was everything and could be everything, but not a rut, so Matteo said: "All right."

She put on her coat. "Saturday night? Or have you got something else going?"

"Uh," Matteo said, pretending to think about that one. "No," he said as he showed her to the door. "I don't have any major plans for Saturday night."

"Okay," Shawna said. "So now we've got a major plan. I'll text you my address later on."

Matteo nodded.

"But what about your boyfriend?" he asked, the doorknob in hand.

"He won't be home till late. Come by around nine. I'll be waiting for you."

He gave her a quick kiss, then went to the kitchen to heat a pan of water for the ravioli. He ate only light meals, and preferably the same thing every day.

At eight o'clock on Saturday evening—Matteo hated showing up late—he caught the subway to Brooklyn. He took a newspaper with him, more to hide behind than to read. On an index card he had written the name of the station where he had to get off, and the route he had to follow from there.

He walked slowly, it was still a little too early. A few times he stopped and looked around, and once he had found the right address he circled the block until his watch said five to nine. Then he rang the bell.

The building had no elevator. Not that his building had an elevator.

He climbed the stairs to the sixth floor, where Shawna lived with her boyfriend.

The door was already open.

There was a doormat with "Welcome" written on it. "Hello," he called out, wiping his feet.

"Come in," Shawna said.

She led him into the kitchen.

"What would you like to drink?" she asked.

She opened the refrigerator and said: "Actually, beer's all I've got."

"Beer's fine," Matteo said.

She took a big beer glass out of the freezer and filled it.

"What are you having?" he asked.

"I already poured myself a beer."

They went into the living room. There was a couch, and a big plasma set on the wall.

It was the biggest plasma screen Matteo had ever seen.

"Want to watch a movie?" Shawna asked.

Matteo thought that was a good idea.

She put on a movie. It was Japanese. Matteo slowly sank down into the cushions. He was tired, without knowing why. Whatever it was, he needed to get going on that scientific research. How long could he keep putting it off? One of his colleagues had said to him: "You're addicted to bullshit."

It was an off-the-cuff remark, probably quite innocent, but a remark Matteo could not forget.

"This is different, isn't it?" Shawna said. "It really was becoming a little bit of a rut."

"What kind of work does your boyfriend do, anyway?" Matteo asked.

"He's a cook."

Shawna unzipped Matteo's trousers.

"I guess he really likes to cook then," Matteo said.

"No," Shawna said. "Not at all."

At that moment the door swung open. There stood a tall, skinny young man in a cap. He was holding a baseball bat.

"You're dead now!" he shouted at Matteo.

Matteo stood up and tried to fasten his trousers.

He saw everything clearly. His scientific research, politics, his life, but also the furniture and the objects in the room. The colors seemed more intense.

"You're dead now!" the man with the bat shouted again, and raised it over his shoulder.

Matteo put his hands on his head and waited for the bat to hit them.

Shawna was right about one thing: this was not a rut.