I said nothing, but I had a sense that Petro's night of triumph had just been spoiled.

The freedmen had taken all the luggage on to the ship. They stayed aboard. We could see sailors assuming their places at the mooring ropes. The captain hovered at the head of the gangplank, impatient to sail now he had the breeze and approaching light. None of us made any attempt to look for Linus. It was best to forget he was there.

The vessel was a roomy merchantman called the Aphrodite. Balbinus would be well set up; there was a cabin for the captain and favoured passengers; a latrine hanging over the stern, even a galley where food could be prepared. The Aphrodite was half as big again as the ship on which Helena and I had returned from Syria. She needed to be strongly built to make such a long voyage so late in the year.

Now the criminal stood looking hesitant; he seemed uncertain what was expected of him. `Am I to board?'

His doubt did not last. Petronius Longus appeared in front of him, flanked by Martinus and me. The other squad members clustered close, in a tight circle.

`Just a few formalities.' It was clear that now Balbinus was in the care of the Fourth Cohort there would be no hail-fellow handshaking. `I've waited a long time, Balbinus,' Petro said.

`No doubt you have done your duty, officer.' The man spoke with reproach. He still seemed like a tunic-braid salesman – one who had just been told to his amazement that his embroidered Egyptian fancies had leaked crimson dye all over ten togas at some swanky laundry. `I am innocent of the crimes of which I have been accused.'

`They all say that,' Petronius complained, addressing the sky in despair. `Gods, I hate this hypocrisy! A straight villain always respects a straight arrest. He'll shrug and accept that he's caught. But all you self-justifying types have to make out that you cannot believe anyone could so terribly misjudge you. You convince yourselves all that matters in a civilised society is for men like you to continue your businesses without interference from officious sods like us. Sods who don't understand.' Petronius set his jaw so hard I thought I heard his molars crunch. 'Only I do understand!' he sneered. `I understand what you are all too well.'