Knox and Peterson made their way up the dim staircase to the top floor. Peterson watched his step as they plunged into darkness between landings, making sure he never came close to touching the walls, the banister, or the half-hidden bits of detritus littering the stairs.

The higher they got, the more stale and warm the air became. At first, Knox thought this was just a lack of airflow in the old building conspiring with the summer afternoon heat. But, as they walked down the short corridor to the only open door, he began to suspect otherwise. And, as Peterson stepped into the flat ahead of him and doubled over, retching, his suspicion was confirmed.

In the hallway of the flat were two bodies. The odour was now pungent, acrid, familiar. Knox had seen, and smelled, death enough during the war to not be shocked by it now. Apparently Peterson hadn’t. Whoever these people were, they’d been lying there for a while.

Knox was curious about what two dead bodies might have to do with him. He was also curious about why there were no police officers or forensics team present but the acting director general of MI5 was. Gordon Manning emerged from a door at the end of the hallway that ran the length of the flat. He stopped for a moment on the other side of the bodies, looking at Knox and Peterson, then beckoned them to follow him as he ducked back into the room he’d just stepped out of.

Manning was a tall man. Too tall, and thin. He’d never carried either well. The three-piece grey worsted suits he insisted on wearing whatever the weather always hung off his skeletal frame, their jacket pockets bagging slightly from his habit of planting his long, bony hands in them.

Knox looked down at the corpses as he stepped around them. The bodies were neat, lying next to each other, their legs straight and arms by their sides. The men’s clothes were plain, dark, normal. They looked like the type of people you’d pass on the street without noticing, except that their mouths and noses were wet with some kind of liquid and they both had thick marks across their necks.

‘Thank you for coming, Richard,’ Manning said, as Knox stepped into the small room. ‘Though I suspect you’re wondering why you’re here.’

‘Actually, I’m wondering why you’re here, sir,’ Knox replied.

‘Those men out there,’ Manning said. ‘I want to know who killed them.’

‘Why?’ No sir this time.

‘They were troublemakers, Italians,’ he said, as if that was explanation eriough. ‘Camillo Bianchi and Piero Moretti. Liked breaking into electronic systems, then holding people to ransom to find out how they’d done it. Five has been keeping an eye for some time.’