Valens glanced around the landing. It was almost identical to the others. A window faced a door, but this window was shuttered. There was another difference – here a ladder ascended to the roof. Given the inclement weather, the heavy trapdoor to above was shut. The guard on the battlements would be very exposed to the bitter wind.

The guard on the door was in no hurry. He chatted to his colleague before levering himself off the door frame and reaching for his keys.

Odds of two to one against, Valens thought. And there was a third man on the roof. Either Clemens or Iudex would have been a better bet – both were natural killers. But an officer could not send men into danger that he would not face himself.

With luck, the sentinel on the roof would hear nothing above the wind. The trapdoor looked solid.

Strike quickly, take them unaware, and it would be over in moments.

The guard turned the key, and pushed the door open.

The sun was setting over the snow-clad peaks. Its light slanted through the slit window opposite the door. Two figures were silhouetted in the centre of the room. As Valens’s eyes adjusted, he saw a young boy. Standing behind the boy, and a little to one side, was a tall man. The man was beardless and very old.

Who in Hades was the man? He was ancient, but still he made the odds yet worse.

‘Put the tray on the table,’ one of the Persians said.

There were hangings on the wall, and cushions on the rugs on the floor. For some unknowable reason, pieces of kindling were laid out on a rug in almost military precision. A low table stood next to a lit brazier in front of the figures in the middle of the room.

‘We don’t want to stand here all evening.’

Neither of the guards moved to enter the room.

As Valens moved forward, he noted that the old man was sweating, and his eyes were wild.

‘Health and great joy,’ Valens said in Greek.

‘No one speaks to the prisoners,’ one of the guards snapped.

Valens placed the tray on the table.

The aged man was clutching at something under his sleeve. There was a terrible indecision etched on his face.

‘Get a move on.’

It was now or never.

Valens straightened up, turned and went back through the door. The Persian he had followed stepped back to let him out. When he had passed, the other leant in to pull the door shut. Valens reached behind his leg, and slid the dagger from his boot. Not stopping to think, Valens lunged at the man in front, his right fist flashing out. The soldier tried to twist aside, but his back collided with the outer wall. It was not a clean strike. The blade sliced deeply across the man’s stomach. The Persian grunted with pain. He doubled up, his hands going to the wound.