`No one else could have done it. Nonnius was ideal.'

`But he was a Balbinus boy. How did you sew him up?'

`A sad story.' Petro grinned. `He's dying. His doctor had just put the frighteners on. Pool old Nonnius is suffering from terminal rot.'

`Something nasty that people don't talk about?'

`Same as his profession!' Petro snarled. Then he told me the story: `Back in the spring, I just happened to learn that Nonnius had been given notice to quit by his pet medicine man 'Happened?' This seemed a nice coincidence.

Petro was in full flow and not to be sidetracked by my scepticism. `Nonnius gets informed by some pet Aesculapius that he's finished, but the doctor says he'll last longer if he takes care of himself – no worries, lots of pampering -'

`Expensive!' I was beginning to see Petro's reasoning.

`A life of luxury prescribed! So I get to him when he's just reeling from the bad news, I lend a sympathetic ear, then I put it to him he's spent his life running around for Balbinus while that rat lay on a reading couch counting his winnings – and for what? Now seems the time for a spot of levelling… Since Nonnius has to give up the low life, he soon settles on snatching at the high life to compensate. This appeals to the bastard: taking a litter through the Forum, giving orders to slaves through the window and greeting fawning admirers who are hoping for free gifts. Even more than that, suddenly he loves the idea of robbing Balbinus.'

I laughed shortly. `The loyalty of thieves! So he was prepared to testify?'

'In return for the traditional reward.'

`You did a deal?'

`All legal. He appeared before Marponius and twittered like a happy song finch. In return, as a successful prosecutor he can seize a proportion of Balbinus' traceable assets. The only disincentive is that he has to help us trace them. But it's well worth his while to hire accountants. Having been on the money-collecting side himself he knows the occasional fellow with a dodgy abacus, imaginative enough to guess where the loot may be hidden.'