Petronius walked forwards to greet the officers of the Sixth watch who had escorted the man from Rome. I stayed at his shoulder. He introduced Arica and Tibullinus, whom he knew. Tibullinus appeared to be the man in charge. He was a truculent, untidy centurion, and I didn't like him much. With them was Porcius, a young recruit of Petro's who had been formally attached to them as an observer. He lost himself among the rest of the Sixth's enquiry team rather rapidly.

While we were going through the formalities, another couple of horses turned up. Their riders slid down, then they too joined us, openly nodding to Petro.

`What's this?' cried Tibullinus, sounding annoyed, though he tried to hide it. `Checking up? On the Sixth?'

`Far be it from me to slander- the meticulous Sixth!', Petro assured him. He was a devious bastard when he chose. 'Just a couple of lads I told to lend a hand when they'd finished something else. Looks like they only just caught up with you.

Everyone realised his couple of lads had attached themselves to the Sixth and their not-quite prisoner for the whole journey – and that the men of the Sixth had failed to notice they were being tagged. They should have known. It could have been any kind of ambush. We left it at that, before things became too sensitive.

Something was about to happen.

There was a moment's unnatural atmosphere, then everyone straightened and grew watchful. The carriage door creaked as it opened. Then Balbinus emerged.

V

ALWAYS THE SAME shock: you come face to face with a murderous master criminal, and he looks like a ribbon-seller. Balbinus Pius was five feet three digits – definitely not tall. He was looking me in the windpipe, and appeared not to notice that most of the officers present overstripped him by almost a foot. He had an oval head; an expressionless face; wavering eyes; an anxious expression that verged nicely on bewilderment. His manner was quiet; no more threatening than a ladybird.