“What time was this?”

“Noon. Exactly.”

They climbed the stairs.

She went on: “I had just reached the second floor when two men came running towards me.”

“Describe them, please.”

“It all happened too quickly for me to get a very good look. Both in their thirties. One had a brown suit, the other had a green anorak. Short hair. That’s about it.”

“What did they do when they saw you?”

They just pushed past me. The one in the anorak said something to the other, but I couldn’t hear what it was. There was a lot of drilling going on from the elevator shaft. After that, I carried on up to Stuckart’s apartment and rang the bell. There was no reply.”

“So what did you do?”

“I walked down to the porter and asked him to open Stuckart’s door, to check he was okay.”

“Why?”

She hesitated. “There was something about those two men. I had a hunch. You know: that feeling when you knock on a door and nobody answers but you’re sure someone’s in.”

“And you persuaded the porter to open the door?”

“I told him I’d call the police if he didn’t. I said he would have to answer to the authorities if anything had happened to Doctor Stuckart.”

Shrewd psychology, thought March. After thirty years of being told what to do, the average German was careful not to take final responsibility for anything, even for not opening a door. “And then you found the bodies?”

She nodded. The porter saw them first. He screamed and I came running.”

“Did you mention the two men you’d seen on the stairs? What did the porter say?”

“He was too busy throwing up to talk at first. Then he just insisted he’d seen nobody. He said I must have imagined it.”

“Do you think he was lying?”

She considered this. “No, I don’t. I think he genuinely didn’t see them. On the other hand, I don’t see how he could have missed them.”

They were still on the second floor landing, at the point at which she said the men had passed her. March walked back down the flight of stairs. She waited for a moment, then followed him. At the foot of the steps a door led off to the first floor corridor.

He said, half to himself: They could have hidden along here, I suppose. Where else?”

They continued down to the ground floor. Here there were two more doors. One led to the foyer. March tried the other. It was unlocked. “Or they could have got out down here.”

Bare concrete steps, neon-lit, led down to the basement. At the bottom was a long passage, with doors off it. March opened each in turn. A lavatory. A store-room. A generator room. A bomb shelter.

Under the 1948 Reich Civil Defence Law, every new building had to be equipped with a bomb shelter; those beneath offices and apartment blocks were also required to have their own generators and air-filtration systems. This one was particularly well-appointed: bunk beds, a storage cupboard, a separate cubicle with toilet facilities. March carried a metal chair across to the air vent, set into the wall two and a half metres above the ground. He grasped the metal cover. It came away easily in his hands. All the screws had been removed.

The Ministry of Construction specifies an aperture with a diameter of half a metre,” said March. He unbuckled his belt and hung it and his pistol over the back of the chair. “If only they appreciated the difficulties that gives us. Would you mind?”

He took off his jacket and handed it to the woman, then mounted the chair. Reaching into the shaft, he found something hard to hold on to, and pulled himself in. The filters and the fan had both been removed. By working his shoulders against the metal casing he was able to move slowly forwards. The darkness was complete, He choked on the dust. His hands, stretched out in front of him, touched metal, and he pushed. The outside cover yielded and crashed to the ground. The night air rushed in. For a moment, he felt an almost overpowering urge to crawl out into it, but instead he wriggled backwards and lowered himself into the basement shelter. He landed, dusty and grease-smeared.

The woman was pointing his pistol at him.

“Bang, bang,” she said. “You’re dead.” She smiled at his alarm: “American joke.”

“Not funny.” He took the Luger and put it back in his holster.

“Okay,” she said, “here’s a better one. Two murderers are seen by a witness leaving a building and it takes the police four days to work out how they did it. I’d say that was funny, wouldn’t you?”

“It depends on the circumstances.” He brushed the dust off his shirt. “If the police found a note beside one of the victims in his own handwriting, saying it was suicide, I could understand why they wouldn’t bother looking any further.”

“But then you come along and you do look further.”

“I’m the curious type.”

“Clearly.” She smiled again. “So Stuckart was shot and the murderers tried to make it look like suicide?” He hesitated. “It’s a possibility.”

He regretted the words the moment he uttered them. She had led him into disclosing more than was wise about Stuckart’s death. Now a faint light of mockery played in her eyes. He cursed himself for underrating her. She had the cunning of a professional criminal. He considered taking her back to the bar and going on alone, but dismissed the idea. It was no good. To know what had happened, he needed to see it through her eyes.

He buttoned his tunic. “Now we must inspect Party Comrade Stuckart’s apartment.”

That, he was pleased to see, knocked the smile off her face. But she did not refuse to go with him. They climbed the stairs, and it struck him again that she was almost as anxious to see Stuckart’s flat as he was.

They took the elevator to the fourth floor. As they stepped out, he heard, along the corridor to their left, a door being opened. He grabbed the American’s arm and steered her round the corner, out of sight. When he looked back, he could see a middle-aged woman in a fur coat heading for the elevator. She was carrying a small dog.

“You’re hurting my arm.”

“Sorry.” He was hiding from shadows. The woman talked quietly to the dog and disappeared into the lift. March wondered whether Globus had retrieved the file from Fiebes yet, whether he had discovered that the keys were missing. They would have to hurry.

The door to Stuckart’s apartment had been sealed that day, close to the handle, with red wax. A note informed the curious that these premises were now under the jurisdiction of the Geheime Staatspolizei, the Gestapo, and that entry was forbidden. March pulled on a pair of thin leather gloves and broke the seal. The key turned easily in the lock.

He said: “Don’t touch anything.”

More luxury, to match the building: elaborate gilt mirrors, antique tables and chairs with fluted legs and ivory damask upholstery, a carpet of royal blue with Persian rugs. The spoils of war, the fruits of Empire.

“Now tell me again what happened.”

“The porter opened the door. We came into the hall.” Her voice had risen. She was trembling. “He shouted and there was no reply, so we both came right in. I opened that door first.”

It was the sort of bathroom March had seen only in glossy magazines. White marble and brown smoky mirrors, a sunken bathtub, twin basins with gold taps… Here, he thought, was the hand of Maria Dymarski, leafing through German Vogue at the Ku-damm hairdressers, while her Polish roots were bleached Aryan white.

Then, I came into the sitting room…”

March switched on the light. One wall consisted of tall windows, looking out over the square. The other three had large mirrors. Wherever he turned, he could see images of himself and the girl: the black uniform and the shiny blue coat incongruous among the antiques. Nymphs were the decorative conceit. Fashioned in gilt, they draped themselves around the mirrors; cast in bronze, they supported table lamps and clocks. There were paintings of nymphs and statues of nymphs; wood nymphs and water nymphs; Amphitrite and Thetis.