Saturnalia was a good time for a family quarrel; it could easily be lost among the seasonal rumpus. But not this quarrel, unfortunately.

Helena Justina played down the incident for as long as Pa stayed around. Neither of us told him any more gossip. Eventually he gave up. The minute he left, she pulled on a warm cloak, called up a carrying chair, and rushed off to confront her brother at their late uncle's empty, elegant house by the Capena Gate. I did not bother to go with her. I doubted she would find Justinus there. He had enough sense not to place himself in a losing position, like a doomed counter on a backgammon board, right where furious female relatives could jump on him.

My darling wife and mother of my children was a tall, serious, sometimes obstinate young woman. She described herself as 'a quiet girl', at which I openly guffawed. Still, I had heard her describe me to strangers as talented and of fine character, so Helena had good judgement. More sensitive than her outward calm revealed, she was so upset about her brother she failed to notice that a messenger from the imperial Palace had come for me. If she had realised, she would have been even more jumpy. It was the usual washed-out slave. He was underdeveloped and rickety; he looked as if he had stopped growing when he hit his teens, though he was older than that – had to be, to become a trusty who was sent out alone on the streets with messages. He wore a crumpled loose-weave tunic, bit his dirty nails, hung his lousy head, and in the customary manner, claimed to know nothing about his errand. I played along. 'So what does Laeta want?' 'Not allowed to say.' 'Then you admit it is Claudius Laeta who sent you to get me?' Out-manoeuvred, he cursed himself 'fair do's, Falco… He's got a job for you.'

'Will I like it? – Don't bother answering.' I never liked anything from the Palace. 'I'll fetch my cloak.'

We buffeted our way through the Forum. It was packed with miserable householders, taking home green boughs for decoration, depressed by the inflationary Saturnalia prices and by knowing they were stuck with a week when they were supposed to forget grudges and quarrels. Four times I rebuffed hard-faced women selling wax candles from trays. Drunks were already littering the temple steps, celebrating in advance. We had nearly two weeks to get through yet. I had worked on imperial missions before, usually abroad. These jobs were always terrible and complicated by ruthless scheming among the Emperor's ambitious bureaucrats. Half the time their dangerous in-fighting threatened to ruin my efforts and get me killed.

Though designated a scroll secretary, Claudius Laeta ranked high; he had some undefined oversight of both home security and foreign intelligence. His only good point, in my opinion, was that he endlessly struggled to outwit, out-manoeuvre, out-stay and do down his implacable rival, Anacrites the Chief Spy. The Spy worked alongside the Praetorian Guard. He was supposed to keep his nose out of foreign policy, but he meddled freely. He possessed at least one extremely dangerous agent in the field, a dancer called Perella, though generally his sidekicks were dross. Up to now, that had given Laeta the upper hand.

Anacrites and I had occasionally worked together. Don't let me give the impression I despised him. He was a festering fistula of pestilential pus. I treat anything that venomous only with respect. Our relationship was based on the purest emotion: hate.

Compared with Anacrites, Claudius Laeta was civilised. Well, he looked harmless as he rose from a couch to greet me in his highly painted office, but he was a silken-tongued twister I had never trusted. He saw me as a grimy thug, though a thug who possessed intelligence and other handy talents. We dealt with one another, when we had to, politely. He realised that two of his three masters – the Emperor himself and the elder of Vespasian's sons, Titus Caesar – both had a high regard for my qualities. Laeta was far too astute to ignore that. He held on to his position by the old bureaucrat's trick of feigning agreement with any views his superiors held strongly. He only stopped short of the pretence that hiring me had been his recommendation. Vespasian could spot that sort of creep.

I was quite sure that Laeta had managed to find out that the younger princeling, Domitian Caesar, had a deep-running feud with me. I knew something about Domitian that he would dearly love to expunge: he once killed a young girl, and I still possessed the evidence. Outside the imperial family it remained a secret, but the mere fact that such a secret existed was bound to reach their sharp-eyed chief secretaries. Claudius Laeta would have buried a coded note in some scroll in his columbarium, reminding himself to use my dangerous knowledge against me one day.

Well, I had information on him too. He schemed too much to stay in the clear. I wasn't worried. Despite this plotting and jealousy, the old Palace of Tiberius always seemed surprisingly fresh and businesslike. The Empire had been run from this fading monument for a century, through good emperors and debauched ones; some of the slick slaves went back here for three generations. The messenger had dropped me off almost as soon as we entered through the Cryptoporticus. With barely a wave of a spear from the guards, I wound my way up into the interior, through staterooms I recognised, and on into ones I could not remember. Then I hit the system.

An invitation was no guarantee of a welcome. As usual, working through the flunkeys was a frustrating grind. Vespasian had famously abandoned the paranoid security Nero used to protect himself from assassination: now, nobody was searched. It may have impressed the public; I knew better. Even our most lovable old emperor since Claudius was too shrewd to take risks. Power draws lunatics. There would always be one crackpot ready to run amok with a sword in the perverted hope of fame. So as I sought Laeta's office I was pushed around by Praetorian Guards, held up while chamberlains consulted lists upon which I did not feature, stuck alone in corridors for hours, and generally driven crazy. At which point Laeta's tidily dressed minions had let me in. 'Next time you want me, let's meet on a park bench!' 'Didius Falco! How pleasant to see you. Still frothing at the mouth, I see.'

Arguing was about as useful as demanding a recount of your change in a busy lunchtime food bar. I forced myself to simmer down. Laeta saw he had nearly pushed me too far. He caved in. 'So sorry to keep you waiting, Falco. Nothing changes here. Too much to do and too little time to do it – and a panic on, naturally.'

'I wonder what that can be!' I implied I had private information about it. I didn't. 'I'll come to that -' 'Keep it brisk then.' 'Titus Caesar suggested I talk to you -' 'And how is the princely Titus?' 'Oh – wonderful, wonderful.' 'Still screwing beautiful Queen Berenice? Or have you dreamed up some stratagem to whisk her back to her desert and avert embarrassment?'

Nursemaids must give a potion in babies' little pottery feeding bottles, one that makes aristocratic Roman males hanker after exotic women. Cleopatra had worked her way through enough Roman top brass. Now Titus Caesar, like me a handsome lad in his thirties, was an amiable prince who ought to be marrying a fifteen-year-old pretty patrician with good hips so he could father the next generation of Flavian emperors; instead, he preferred to dally on purple cushions with the voluptuous Queen of Judaea. It was true love, they said. Well, it must certainly be love on his part; Berenice was hot stuff, but older than him, and had a terrible reputation for incest (which Rome could cope with) and political interference (which was bad news). Conservative Rome would never accept this hopeful dame as an imperial consort. Astute in all other matters, Titus stuck with his no brain love affair like some bloody-minded teenager who had been instructed to stop smooching the kitchen maid.