The clerks never pay up, but barmen can be useful. A private informer can spend weeks looking for lost women, then, when he gets tired of putting his feet in wineshops (if ever), he only has to point out to the client that missing waitresses are generally found with their heads bashed in, hidden under their boyfriends' floorboards at home. This generally gets the bills for surveillance paid ultra-promptly, and sometimes the barmen even leave town for a long period afterwards-a bonus for Rome. I like to feel my work has community value.

Of course a barman can be disastrous. The girlfriend may be genuinely missing, having run off with a gladiator, so you still spend weeks searching, only to end up feeling so sorry for the dumb cluck who has lost his tawdry turtle-dove that you can't bring yourself to ask him for your fee:

I went to the baths for a spot of exercise with my trainer, just in case I did manage to land myself a case which required putting myself out. Then I looked for my friend Petronius Longus. He was captain of the Aventine Watch, which involved dealing with all types, many of them the unscrupulous variety who might need my services. Petro often sent work my way, if only to avoid having to deal with tiresome characters himself.

He was not in any of his usual haunts, so I went to his house. All I found there was his wife-an unwelcome treat. Arria Silvia was a slightly built, pretty woman; she had small hands and a neat nose, with soft skin and fine eyebrows like a child's. But there was nothing soft about Silvia's character, one aspect of which was a searing opinion of me.

'How's Helena, Falco? Has she left you yet?'

'Not yet.'

'She will!' promised Silvia.

This was banter, though fairly caustic, and I treated it warily. I left a message to tell Petro I was light in the occupation stakes, then hotfooted out of it.

While I was in the area I dropped in at my mother's; Ma was out visiting. I was not in the mood for hearing my sisters bemoaning their husbands, so I gave up on my relations (not a hard decision) and went home.

A worrying scene greeted me. I had crossed the stinking alley towards Lenia's laundry, the cut-price, clothes-stealing wash-shop which occupied the ground floor of our building, when I noticed a set of tough tykes bristling with buckles who were standing about the stairwell trying to act inconspicuous. A hard task to set themselves: the battle scenes on their breastplates were polished to a dazzle that would stop a water-clock, let alone a passer-by, and ten determined children had stationed themselves in a circle to gape at their scarlet helmet plumes and dare one another to try and poke sticks between the mighty mens' bootstraps. It was the Praetorian Guard. The whole Aventine must know that they were here.

I could not remember having done anything lately that the military might object to, so I assumed an innocent saunter and kept going. These heroes were out of their own refined environment and looking pretty jumpy. I was not surprised to be stopped at the steps by two spears slamming together across my chest.

'Steady, lads, don't snag my outfit-this tunic still has a few decades of life in it:'

A laundry girl barged out of the steam with a sneer on her face and a basket of particularly disgusting unwashed goods. The sneer was for me.

'Friends of yours?' she scoffed.

'Don't insult me! They must have been going to arrest some troublemaker and lost their way:'

They were obviously not here to apprehend anybody. Some lucky citizen in this sordid part of society was no doubt being visited by a member of the imperial family, incognito apart from the vivid presence of his bodyguard.

'What's going on?' I asked the centurion in charge.

'Confidential-move along!'

By now I had guessed who the victim was (me) and the reason for the visitation (cajoling me into the mission in Germany Momus had warned me about). I felt full of foreboding. If the mission was so special or so urgent it demanded such personal treatment, it must involve the kind of effort I would really hate. I paused, wondering which of the Flavians was venturing his princely toes in our alley's pungent mud.

The Emperor himself, Vespasian, was too senior and too sensitive about status to make free with the populace. Besides, he was over sixty. At my house he would never manage the stairs.

I had crossed paths with his younger son, Domitian. I once exposed a piece of dirty work by the junior Caesar, which now meant that Domitian would like to see me wiped off the earth, and I felt the same about him. However, we ignored each other socially.

It must be Titus.

'Titus Caesar come to see Falco?' He was impetuous enough to do it. Letting the officer know that I despised official secrecy, I lifted apart the impressively polished spear tips with one delicate finger. 'I'm Marcus Didius. Better pass me in so I can hear what joys the bureaucracy are planning for me now:'

They let me through, though with a sarcastic look. Perhaps they had been assuming their heroic commander had lowered himself for an off-colour intrigue with some Aventine wench.

Making no attempt to hurry, since I was a fervent republican, I took myself upstairs.

When I went in, Titus was talking to Helena. I stopped short abruptly. The look I had seen the Praetorians exchange began to make more sense. I began to think I had been a fool.

Helena was sitting out on the balcony, a small affair which clung perilously to the side of our building, its old stone supports held on mainly by twenty years of grime. Although there was room for an informal type like me to share the bench with her, Titus had remained politely standing beside the folding door. Ahead of him lay a spectacular view of the great city which his father ruled, but Titus was ignoring it. In my opinion, with Helena to look at, anybody would. Titus shared my opinion pretty openly.

He was the same age as me, a curly-haired optimistic type who would never be soured by life. In my unmajestic billet here, the crusted gold palm leaves embroidering his tunic made an incongruous show, yet Titus managed not to seem out of place. He had an attractive personality and was at home wherever he went. He was pleasant, and for a top-ranker, cultured to his sandalstraps. He was an all-round political achiever: a senator, a general, Commander of the Praetorians, a benefactor of civic buildings, a patron of the arts. On top of that, he was good-looking. I had the girl (though we did not declare it in public); Titus Caesar had everything else.

When I first saw him talking to Helena, his face had a pleased, boyish expression which made my teeth set. He was leaning on the door with his arms folded, unaware that the hinges were quite likely to give way. I hoped they would. I wished they would dump Titus in his splendid purple tunic flat on his back on my ramshackle floor. In fact the moment I saw him there, in deep conversation with my girlfriend, I sank into a mood where almost any sort of treason seemed a bright idea.

'Hello, Marcus,' said Helena-paying far too much attention to putting on a neutral face.