“A heart attack? Some kind of seizure?”

“Possible,” admitted Eisler. Eck handed him a scalpel. “I won’t know until I’ve completed a full examination of the internal organs.”

“How long will that take?”

“As long as it takes.”

Eisler positioned himself behind Buhler’s head. Tenderly, he stroked the hair towards him, off the corpse’s forehead, as if soothing a fever. Then he hunched down low and jabbed the scalpel through the left temple. He drew it in an arc across the top of the face, just below the hairline. There was a scrape of metal and bone. Eck grinned at them. March sucked a lungful of smoke from his cigar.

Eisler put the scalpel into a metal dish. Then he bent down once more and worked his forefingers into the deep cut. Gradually, he began peeling back the scalp. March turned his head away and closed his eyes. He prayed that no one he loved, or liked, or even vaguely knew, ever had to be desecrated by the butcher’s work of an autopsy.

Jaeger said: “So what do you think?”

Eisler had picked up a small, hand-sized circular saw. He switched it on. It whined like a dentist’s drill.

March took a final puff on his cigar. “I think we should get out of here.”

They made their way down the corridor. Behind them, from the autopsy room, they heard the saw’s note deepen as it bit into the bone.

Half an hour later, Xavier March was at the wheel of . one of the Kripo’s Volkswagens, following the curving path of the Havelchaussee, high above the lake. Sometimes the view was hidden by trees. Then he would round a bend, or the forest would thin, and he would see the water again, sparkling in the April sun like a tray of diamonds. Two yachts skimmed the surface — children’s cut-outs, white triangles brilliant against the blue.

He had the window wound down, his arm resting on the sill, the breeze plucking at his sleeve. On either side, the bare branches of the trees were flecked with the green of late spring. In another month, the road would be nose-to-tail with cars: Berliners escaping from the city to sail or swim, or picnic, or simply to lie in the sun on one of the big public beaches. But today there was still enough of a chill in the air, and winter was still close enough, for March to have the road to himself. He passed the red-brick sentinel of the Kaiser Wilhelm Tower and the road began to drop to lake level.

Within ten minutes he was at the spot where the body had been discovered. In the fine weather it looked utterly different. This was a tourist spot, a vantage-point known as the Grosse Fenster: the Picture Window. What had been a mass of grey yesterday was now a gloriously clear view, across eight kilometres of water, right up to Spandau.

He parked, and retraced the route Jost had been running when he discovered the body — down the woodland track, a sharp right turn, and along the side of the lake. He did it a second time; and a third. Satisfied, he got back into the car and drove over the low bridge on to Schwanenwerder. A red and white pole blocked the road. A sentry emerged from a small hut, a clipboard in his hand, a rifle slung across his shoulder.

“Your identification, please.”

March handed his Kripo ID through the open window. The sentry studied it and returned it. He saluted. “That’s fine, Herr Sturmbannfuhrer.”

“What’s the procedure here?”

“Stop every car. Check the papers and ask where they’re going. If they look suspicious, we ring the house, see if they’re expected. Sometimes we search the car. It depends whether the Reichsminister is in residence.”

“Do you keep a record?”

“Yes, sir.”

“Do me a favour. Look and see if Doctor Josef Buhler had any visitors on Monday night.”

The sentry hitched his rifle and went back into his hut. March could see him turning the pages of a ledger. When he returned he shook his head. “Nobody for Doctor Buhler all day.”

“Did he leave the island at all?”

“We don’t keep a record of residents, sir, only visitors. And we don’t check people going, only coming.”

“Right.” March looked past the guard, across the lake. A scattering of seagulls swooped low over the water, crying. Some yachts were moored to a jetty. He could hear the clink of their masts in the wind.

“What about the shore. Is that watched at all?”

The guard nodded. "The river police have a patrol every couple of hours. But most of those houses have enough sirens and dogs to guard a KZ. We just keep the sightseers away.”

KZ: pronounced kat-set. Less of a mouthful than Konzentrationslager. Concentration camp.

There was a sound of powerful engines gunning in the distance. The guard turned to look up the road behind him, towards the island.

“One moment, sir.”

Round the bend, at high speed, came a grey BMW with its headlights on, followed by a long black Mercedes limousine, and then another BMW. The sentry stepped back, pressed a switch, the barrier rose, and he saluted. As the convoy swept by, March had a glimpse of the Mercedes’s passengers — a young woman, beautiful, an actress perhaps, or a model, with short blonde hair; and, next to her, staring straight ahead, a wizened old man, his rodent-like profile instantly recognisable. The cars roared off towards the city.

“Does he always travel that quickly?” asked March.

The sentry gave him a knowing look. “The Reichs-minister has been screen-testing, sir. Frau Goebbels is due back at lunchtime.”

“Ah. All is clear.” March turned the key in the ignition and the Volkswagen came to life. “Did you know that Doctor Buhler was dead?”

“No, sir.” The sentry gave no sign of interest. “When did that happen?”

“Monday night. He was washed up a few hundred metres from here.”

“I heard they’d found a body.”

“What was he like?”

“I hardly noticed him, sir. He didn’t go out much. No visitors. Never spoke. But then, a lot of them end up like that out here.”

“Which was his house?”

“You can’t miss it. It’s on the east side of the island. Two large towers. It’s one of the biggest.”

“Thanks.”

As he drove down the causeway, March checked in his mirror. The sentry stood looking after him for a few seconds, then hitched his rifle again, turned and walked slowly back to his hut.

Schwanenwerder was small, less than a kilometre long and half a kilometre wide, with a single loop of road running one-way, clockwise. To reach Buhler’s property, March had to travel three-quarters of the way round the island. He drove cautiously, slowing almost to a halt each time he glimpsed one of the houses off to his left.

The place had been named after the famous colonies of swans which lived at the southern end of the Havel. It had become fashionable towards the end of the last century. Most of its buildings dated from then: large villas, steep-roofed and stone-fronted in the French style, with long drives and lawns, protected from prying eyes by high walls and trees. A piece of the ruined Tuileries Palace stood incongruously by the roadside — a pillar and a section of arch carted back from Paris by some long-dead Wilhelmine businessman. No one stirred. Occasionally, through the bars of a gate, he saw a guard dog, and — once — a gardener raking leaves. The owners were either at work in the city, or away, or lying low.

March knew the identities of a few of them: Party bosses; a motor industry tycoon, grown fat on the profits of slave labour immediately after the war; the managing director of Wertheim’s, the great department store on Potsdamer Platz that had been confiscated from its Jewish owners more than thirty years before; an armaments manufacturer; the head of an engineering conglomerate building the great Autobahnen into the eastern territories. He” wondered how Buhler could have afforded to keep such wealthy company, then he remembered Halder’s description: luxury like the Roman Empire …