Surveillance could not be easy. My house had no side or back approaches. The front looked straight out across the Tiber over the Transtiberina slums, towards the old Naumachia where Augustus had staged mock-sea-battles. Nobody here kept topiary in terracotta pots, suitable to hide behind, because if we did night-time drunks just rolled them over the road and pushed them in the river. Occasionally carts were parked, but as the Embankment was a main thoroughfare and a commercial artery, the street aediles had them moved to avoid congestion. All an observer could do was hang around in the road chewing a bread roll, hoping I would not appear in person and spot him. Last time the two so-called Melitans were watching us, the whole family used to wave at them as we came and went. Even the dog once ran up to wag her tail and say hello.

Albia was right. He was there. One of them, on his own. I wondered where his brother was. Maybe the two agents were taking turns—or if Anacrites was thoroughly obsessed with us, the other might be outside Petro and Maia’s apartment. We would have to find out. My sister would become hysterical if she thought the spy was having her watched.

What we did next was totally unplanned. Petronius and I had been in this kind of dark situation once before, in Britain. An officer who betrayed our legion had to be dealt with. Justice was done. Maybe it gave us a taste for hard revenge. I for one had hoped we’d never find ourselves in such a situation again, but when we ended up here on the Embankment with the spy’s agent, neither Petro nor I thought twice.

The man saw me coming, as I walked directly up to him. He was considering resistance when Petro tapped him on the shoulder from behind. We were already too close for him to run or fight. So we had him. We simply took him into custody.

At the time we presumed he thought Anacrites would rescue him. Perhaps he did think that. Perhaps we did. He may have expected we would merely argue about the surveillance, at worst throw a few punches, then order him to stop harassing me. That may even have been what we initially intended.

We searched him. It was no surprise to find that he was carrying: four knives of different sizes plus a short piece of rope that was only suitable for strangulation. We kept him standing in the road while we stripped him of this armoury, not bothering to be polite, though since it was a public place, we were not particularly brutal. He grunted a bit. Petro and I were feeling our way towards a decision.