At the top, on the walkway, Volusianus took a moment to get his breath back. There was a fountain in the courtyard below. Apart from the splashing water it was empty and quiet. The uproar at the gates was at a distance.

The frumentarius who had been placed in the household of Acilius Glabrio led them swiftly through the maze of the huge villa. Once or twice servants peeped out from behind half-open doors, but then vanished. Volusianus followed through opulent halls and libraries, and down mean service corridors, until they came to the dining room. Lights and noise issued from behind the curtains.

As before, Volusianus indicated the others should precede him.

There was an outcry when the armed men burst through the hangings.

Volusianus drew his blade before stepping through.

The conspirators were motionless, like a tableau: the two senators frozen in the act of throwing documents into a brazier, the pair of officers facing the opening with swords in their hands.

For a heartbeat or two no one moved. Then one of the officers shouted something incomprehensible, and both armed men hurled themselves at Murena and the Praetorians.

‘Take one of them alive!’ Volusianus shouted.

Through the clatter of the fight Volusianus saw Acilius Glabrio drop the papyri in his hands and bolt through a small door at the rear of the room. The other senator did not think to follow, but fell to his knees, holding his hands out in supplication.

Unarmoured and outnumbered two to one, the officers had no chance. One of them was clutching his stomach, trying to hold in his own entrails. The other was being wrestled to the ground.

Volusianus moved to the cowering senator.

‘Have no fear, Thrasea. I know what you have done.’

The senator whimpered with terror. Volusianus took his hands, gently raised him up.

‘Your loyalty to the Emperor is an example to us all,’ Volusianus said. ‘It took courage to infiltrate the conspiracy.’

A desperate hope dawned in the senator’s eyes. ‘Yes, that was it. I did not know who to trust, so I told no one.’

‘And now you can tell everything,’ Volusianus said gently.

‘Everything . . . that was always my intention.’

‘Later tonight, my friend.’

Volusianus released the senator’s hands, and looked over his shoulder. The Praetorians were still struggling with the officer who was not mortally wounded.

‘Where does the passage go?’ he asked the frumentarius.

‘Just to the roof garden.’

‘Good. Stay with the senator. Murena, with me.’

Volusianus was blowing hard when he reached the roof garden. After the stairs it was bright in the starlight. Acilius Glabrio was by the balustrade at the far end. Out beyond the villa the grounds were lit by the torches of the troops.

Volusianus put out a hand to stop Murena when he went to apprehend the fugitive.

‘It is over,’ Volusianus said. ‘There is nowhere to run.’

‘You jumped-up peasant,’ Acilius Glabrio spat. ‘You sent my cousin to his death.’