A dead man in the dining car. Six hours to Salzburg.

The train pulled out of Kufstein twenty minutes ago, and the snow has come down so thickly since that the windows show you nothing but your own reflection.

The dining car is too warm. A waiter clears two plates; somebody laughs too loudly at a joke you did not hear. You have taken the last table, because from there you can see the whole car, and it is a habit you are never going to lose.

Then the man at the window table pitches forward.

It happens without a sound. His head hits the tablecloth, the wine bottle starts to slide, and only when it bursts on the floor does half the car turn round. A woman stands up and immediately sits down again. The waiter simply stops, plates still stacked against his chest.

You are beside the man before you have decided to move. The skin at his neck is still warm. There is no pulse. In front of him stands a half-empty glass, beside it a second that nobody has touched, and on the cloth lies a book of matches stamped with the crest of a hotel in Vienna.

The conductor shoulders through the far door. Behind him, out in the corridor, the corner of a coat disappears towards the sleeping cars — someone who did not want to stay and watch.

This train does not stop before Salzburg. Six hours. And everyone it could have been is sitting in the carriage with you.

The conductor wants you to stand up. You stay where you are, and tell him to let nobody out of this car.

The second glass is dry. Not empty — dry. No film inside it, no ring, nothing. It has stood there all evening without anyone drinking from it. The waiter says the gentleman asked for two glasses as soon as he boarded at Innsbruck, and explained nothing.

The matchbook carries the crest of the Hotel Regina on the outside. Inside, in pencil, in a very small hand: Car 7, Comp 3.

There is a ticket in his coat pocket. Salzburg to Vienna, tonight, three twenty. He never meant to arrive anywhere. He meant to turn round in Salzburg and travel straight back.

"Lindner," the conductor says over your shoulder, like a name he knows too well to enjoy saying. "He travels every month."

Travels. Not travelled.

You look up. At the third table, where the woman sat who stood and immediately sat down again, a napkin lies over a full cup. The seat is empty. Her coat still hangs on the back of it, and the sleeve is wet to the elbow, though it has not rained in here since Innsbruck.

"We'll put him in the luggage van," the conductor says. "As far as Salzburg."

Outside the snow is going sideways now, and the train is slowing without anybody having braked.

You find her in the gangway between cars four and five, where the bellows work in the curve and it is loud enough that you have to shout. She has pulled the window down. Twelve below, and she is standing there in a blouse and skirt, smoking, as though that were the pressing matter.

She does not startle. That is the first thing you notice.

"You got to him quickly," she says. "Quicker than the conductor."

Her name is Hoyer, she says. She knew him slightly, she says — the platform in Vienna, you see people, you nod. And then she says the second glass was hers. That she sat down with him and got up again before he started to drink.

You say nothing. You wait to see whether she notices it herself.

"I didn't know Herr Berger well enough to stay," she says.

The conductor gave a different name.

Behind her, in the corridor of car five, a door falls shut. Someone is moving forward, towards the dining car, at the even pace of a person who knows where they are going.

Then the brakes bite. Not hard, but with no station, no signal, in open country. In about a minute the train will be standing, and anyone who wants to get off can get off.

Frau Hoyer looks past you, towards the sleeping cars, and puts the cigarette out on the window frame.

You take hold of her arm, and she allows it.

"You called him Berger," you say. "The conductor said Lindner."

She looks at you long enough that you begin to think she will not answer at all.

"Which name did he give you first?" she asks.

"Lindner."

"Yes." She nods slowly, almost relieved, as though she had hoped for that and not expected it. "Lindner is in car seven, compartment three. Since Innsbruck. He has not left the carriage."

The train stops. The bellows go quiet, and in the silence the ticking of the heating pipes gets loud. Outside, very close, snow crunches under footsteps — somebody is walking along the train, back to front.

"Then who is the man in the dining car?" you ask.

Frau Hoyer lifts your hand off her arm without hurrying, the way you set aside something you intend to pick up again later.

"That," she says, "is the question you have five hours to answer. I would start before the train moves again."

In the corridor behind her the lights go out. Not flickering, not fading — somebody has thrown a switch.