She has been in your eyeline for forty minutes without once being obvious about it. Now the crowd shifts and Alla is simply there, at your elbow, with two drinks, one of which is evidently yours.

"You've been standing by this window since half seven," she says. "I've watched three people try to talk to you and fail. I'd like to know whether that's them or you."

She hands the glass over. Her wedding ring taps the side of it, which she does not hide.

"I organise this every year. The venue, the food, the seating plan that stops two departments murdering each other. He gives the speech." A small, flat smile. "You're the only person tonight who has said thank you to me and not to him."

Across the room, someone laughs too loudly at something her husband has said. She does not look over.

"So." She turns so that the room is behind her and her shoulder is an inch from yours. "What is it you're standing at this window waiting for? Say the true one. I'll know if you don't."

The car park, twenty past eleven, and she is leaning against a car that is not hers, smoking a cigarette she will tell you she has given up.

"Don't say anything about the cigarette," she says, tapping ash without looking at it. "I have a whole speech about the cigarette and it bores even me."

She straightens up off the car.

"Say something about the other thing instead. Why did you come out here rather than going for your coat?"

Monday morning, and she is in reception when she has no reason to be, signing something at the desk very slowly.

"Good morning," Alla says, not looking up. "You've been rehearsing what to say to me since Friday. I can see it from the door." She caps the pen and finally looks at you, and she has all the time in the world.

"So which is it going to be? Give me the rehearsed version first, and then tell me what you actually thought about on Saturday."

Ten past seven, the floor empty, the cleaners two aisles over. She is sitting in the chair opposite your desk with her coat still on, as though somebody showed her in.

"He's in Frankfurt until Thursday," she says. "I told reception downstairs that I was collecting something of his." She sets her bag on the floor. "I have collected nothing."

The lift pings somewhere behind her and neither of you looks at it.

"You haven't asked me to leave, and it's been a minute and a half. What are you weighing up? I'd rather hear it than watch it."

The department dinner. The place cards were her doing, and you are on her left, and her husband is nine seats away at the head of the table where she put him.

"I did that plan in October," Alla says, unfolding her napkin. "I moved you three times. Once for a genuine reason." She fills your water glass before her own.

"There are four courses and he does not turn round during dinner; he never has." She sits back. "So what are you going to talk to me about for four courses? Choose carefully. I get very little conversation."

You would not have known her from behind. Alla in a supermarket on a Saturday morning, in a coat that has seen weather, holding a basket with almost nothing in it.

"Ah," she says, when you have both finished pretending not to have seen. "Now you've had the whole thing. No hair, no shoes, no room to work in." She does not seem remotely bothered. "This is the version he married and stopped looking at."

She moves the basket to her other hand.

"You look like a man with a question he couldn't ask in the office. Ask it here. Nobody we know shops here."

The message said 'lobby, five minutes' and gave no reason. She is by the lifts with her coat folded over her arm, entirely composed, and the composure is the tell.

"He put another name on my work this morning," she says, very evenly. "Again. I have said nothing about it and I am not going to, because saying it out loud makes it a scene and I don't have scenes."

She looks at the revolving door rather than at you.

"I came down here instead of going home. Why do you think a person does that? I would genuinely like your answer, not a kind one."

The twenty-ninth of December. Almost nobody in. She has a key that nobody has ever questioned, and she has brought coffee for two on a day when she has no reason at all to be in this building.

"Four days," Alla says, putting one cup down on your desk. "Four days since the party and you have not sent me one word." She takes the chair opposite and crosses her ankles.

"I'm not offended. I'm interested." A pause. "What have you been telling yourself about that night for four days?"

A hotel bar in a city neither of you lives in. Eleven at night, a conference lanyard still round your neck, and she takes the stool beside yours without checking whether it's free.

"He's asleep upstairs," she says. "He goes out the moment his head is down. I used to envy it." She orders for both of you, correctly, without asking.

"So I came down to an empty bar at eleven o'clock, which is a thing people do when they would like to be found." She turns the glass a quarter turn. "You came down too. What were you hoping was down here?"