‘Time to get happy, Hansi,’ he said in a voice that could almost have been kind, as he opened the case, taking out a disposable hypodermic syringe. ‘Happy like you’ve never been happy before …’

Hansi tried to scream, but the younger man rammed a foul-tasting cloth into his mouth before forcing his arm out straight and pulling up his sleeve.

In the fraction of a second before the lethally pure heroin hit his system, Hansi’s eyes darted from one man’s face to the other. The words, I know who you are … I saw you and I know who you are … died on his immobilised tongue under the filthy rag they had stuffed in his mouth. It took only a few seconds for the heroin to invade all that was the meagre presence of Hansi Kraus. As they pulled the rag from his mouth and turned their backs on him, leaving him to die alone, he thought he could smell freshly laundered bedclothes.

Saturday 21 June, 4.00 a.m. Polizeipräsidium, Hamburg.

The atmosphere in the incident room was an odd mix of excitement and exhaustion. In the dead hours before dawn, officers just awoken and those, like Fabel, Maria, Paul and Anna, who had been awake and active all the previous day struggled to shake off the physical tiredness that clung to them, dulling the thrill of closing in on their prey. There was a buzz of voices on telephones, waking disgruntled officials across Europe, from Hamburg to Kiev.

And there, centre stage, enlarged and pinned to the middle of the inquiry board, the cold green eyes of Vasyl Vitrenko, like the malevolently heroic portrait gaze of some eastern-European dictator, stared out defiantly at those who would pursue him. Beside the image of Vitrenko were copies of the images in the barn supplied by his father. When Fabel had first taped the images to the board, a stunned incredulity had temporarily muted the clamour in the room.

Maria, who spoke English reasonably well and a little Russian, had been pursuing by telephone reluctant police officials in Odessa and Kiev. She had also scanned Europol’s and Interpol’s databases, finding a scrap here and there to help assemble a person behind the image on the inquiry board.

Fabel took a moment of comparative quiet in the room to call together the majority of the team, who then waited until their colleagues still on phones concluded their calls.

Fabel stood before the incident board and leaned on the table, pressing his knuckles down onto the polished cherrywood. He took in a sharp breath before starting his debrief of what the Ukrainian had told him. There was a silence in the room, an intense quiet as if the air had been corded and stretched tight, as he repeated the old man’s account of pursuing his son through the mountains and half-desert plains of Afghanistan, following a trail of growing atrocity, culminating in the discovery in the barn. He then outlined what he had learned about the killings in Kiev.