We had been waiting too long. Although nobody said it, we were starting to dread that the big rissole would not show.

The lowlife was called Balbinus.

I had been hearing his name as long as I could remember. It had certainly been notorious when Petronius and I had come home from the army six years before. At that time my old tentmate Petro, being a dutiful type who fancied a good salary, had put himself forward as a public officer; I set up in business alone. He was chasing cabbage thieves through the markets while I was picking through clerks' divorces and tracing stolen art. On the face of it we lived in different worlds, yet we stumbled across the same tragedies and heard the same worrying stories on the streets.

Balbinus was renowned throughout our district as one of the dirtiest underworld organisers ever to gild imperial Rome. The area he terrorised included brothels, wharfside warehouses, the back-doubles on the Aventine slopes, the dark colonnades around the Circus Maximus. He ran jostlers and confidence tricksters; prostitutes and cutpurses; cat burglars and marauding gangs of street beggars with fake blind eyes who could soon spot trouble coming. He kept a couple of safe houses for receiving, set up under the cover of straight businesses. Petronius reckoned that the flow of stolen goods into these dens of illicit commerce rivalled the international trade at the Emporium.

Petro had been trying to nail Balbinus for years. Now, somehow, he had managed to set up a capital charge – and go on to secure a conviction despite all Balbinus' efforts to escape using democratic channels (intimidation and bribes). I had yet to hear the full details. Barely back in Rome from what I liked to describe as a confidential diplomatic mission, I had been roped in tonight as a dependable extra and friend.