Inside, Murena stood motionless for a time surveying the plain, unassuming room. There was a desk, on it a stylus with other writing equipment, two lamps, and a pile of reports. Behind the desk was a chair, two more for visitors in front. Apart from a stand for armour in a corner, there was no other furniture. All the walls were lined with pigeonholes, each stuffed with documents.

As he did every morning, Murena regarded the scene with a quiet satisfaction. Four years previously he had arrived at the camp as a mere army scout. Seconded from the Fourth Scythian Legion, he had carried an important despatch from the east. Its news had been welcome. The generals Odenaethus and Ballista had turned back a Persian invasion, and a pretender had been killed. Enrolment as a centurion of the frumentarii had been Murena’s reward. Now he was promoted to Princeps Peregrinorum, the Leader of the Strangers, commander of the frumentarii. If the Emperor’s spies were imagined as a spiderweb spread out across the empire, Murena sat at its heart, pulling the threads, catching those who whispered plots against Rome or its ruler, luring those who even thought such things to their doom.

Murena liked to arrive early each morning. Recently appointed, there was much for him to master, and every day brought fresh rumours of sedition. His secretary had stacked the documents on his desk. Each was read and considered, some acted upon, all carefully filed. Hanging his cloak on the armour stand – the late spring dawn was still chilly – Murena sat down. He was eager to find new evidence, to uncover more of the alienated and malignant.

No sooner was he sat at his desk, the first papyrus unrolled, than there was a knock at the door.

‘Come.’

‘Visitor for you, sir,’ the guard said.

A tall figure in a hooded cloak entered without waiting to be summoned.

Murena remained seated. His dignity might be slightly affronted, but he was unalarmed. Secrecy was the stock in trade of the frumentarii, and the guards would admit no one without authorisation.

The large man pushed back his hood to reveal a ruddy, broad face.

Murena leapt to his feet. ‘My apologies, sir. I was not expecting you.’

‘No apologies are necessary.’ The weather-beaten man smiled. ‘Do you have any warmed wine? Have them bring three cups. It is as cold as a witch’s tit out there.’

As Murena went out to arrange the drinks, his heart was thumping. A visit from the Praetorian Prefect, unannounced and incognito, would not be undertaken without good reason.

By the time Murena came back into the room, Volusianus had thrown his cloak on the armour stand, and was seated behind the desk. The Praetorian Prefect waved Murena to one of the visitors’ chairs.