I could see this would work. In theory the Praetorian Prefect looked after the Emperor, the Urban Prefect looked after the city by day, and the Prefect of Vigiles controlled the Night Watch; according to their rulebook, the three forces worked in harmony. In fact, there was serious rivalry. Bad feeling went back at least as far as when Emperor Tiberius found himself under threat from the usurper Sejanus, who had the loyalty of the Praetorians. Unable to trust his own imperial guards, Tiberius had cunningly used the vigiles to arrest Sejanus. The Praetorians now liked to pretend it had never happened – but the vigiles never forgot.

'You could also whisper to the Urban Cohorts why their big brothers are stonking all over the city; the Urbans will defend their patch. ' 'Unfortunately our lot are not talking to the Urbans either. But I'd thought of that,' said Petro.

Of course if it became known that I had brought in the vigiles on a confidential, entirely Praetorian matter, my position would be… difficult. I decided I would deal with that if the issue ever arose. I could now trust Petronius to put in place a city-wide search for the priestess. He understood that it needed to be an observation and reporting back exercise, nothing too visible. For all we knew, Veleda might have assembled a support group; they could be armed and plotting trouble. We also had to avoid causing general alarm. I asked Petro for advice on where to start looking myself 'The obvious way to disappear,' he said, 'is for her to get a job in some backstreet bar.'

'Not feasible. She's never been in a city. She's never lived as a free woman anywhere. We call her a barbarian, though she's more sophisticated than you would expect – yet she'll stick out as a stranger. She's always held a position of respect among the tribes; she's been tended and protected – she lived at the top of a signal tower, for heavens' sake – so she won't know anything about normal life. She probably couldn't live alone unnoticed, even in her own country -' 'Does she have any money, Falco?' 'Probably not. She should have been stripped of her valuables. Perhaps some jewellery. I can ask Pa to put the word out in case she tries to sell anything.' Ganna should be able to tell me what Veleda possessed. Anything worthwhile would find its way to the gem stalls at the Saepta Julia. 'I am told she wants to get back to Free Germany. It's the wrong time of year to travel and the alarm is raised. Unless she makes contact with sympathisers who are willing to help her, she can't even pay for the journey.' 'So she has to go underground.' Petro was thinking. He ticked off people I should contact. 'The German community in Rome.' 'Is there one?' He shrugged. 'Traders. Must be. Your father should know, from colleagues at the Emporium.' 'Aren't traders by definition friends of Rome?'

'When were traders friends of anyone but themselves?' Petronius was cynical. 'Traders come from all over the place, you know that. They have no qualms about making money from their nations' enemies. Aliens can get here. There's probably some tight little nest of Bructeran barterers right under our noses, if we knew where to look. But don't ask me.' 'No handy list of Free German interlopers?' Petronius ignored my jibe about vigiles' lists. They kept one for informers, and I knew my name was on it. 'I can't think what the Bructeri would have to sell in Rome.'

'People come here to buy, Falco.' He was right there. He thought of another unpleasant group to search: 'Then assuming your priestess is destitute, she might find a refuge among runaway slaves.'

'And how,' I asked sarcastically, 'do I find them, given that their wronged masters have failed to do so? Aren't they invisible on principle?' 'Plenty out there. Doorways. Under the arches. A large colony sleeps rough among the tombs on the Via Appia.' 'I thought the necropolis was haunted by ghosts?'

'Be bloody careful if you go there!' Petro warned. He did not offer to accompany me, I noticed. 'There's one more place. She is a priestess – you could try looking in temples.'

Oh thanks very much. It must have escaped his notice how many of those there were in Rome.

One of his cats crept into the room. The beast could tell I was a dog man, so it smugly came straight for me, purring. Petronius started grinning. I was already flea-bitten after Stringy at the caupona, so I made my excuses rapidly and went home.

My house seemed suspiciously quiet. It spoke of recent ructions. I didn't ask.

Helena and I sat in the kitchen and organised ourselves a quiet supper. We had the last of today's bread, some cold fish, olives and soft cheese. I scrutinised her carefully, but she seemed at ease. Being landed with the soldiers, in the run up to Saturnalia, failed to faze her. The truth was, Helena Justina liked a challenge.

From a corner of the room, our new cook Jacinthus watched. If he had seemed upset by us invading his territory, we would have let him choose the food and serve us, but he was indifferent. So we took over the scrubbed table where he was supposed to prepare things, I fetched a jug of white wine which we two kept to ourselves, and we carried on discussing the day as we always had done, cook or no cook. I had worked on occasions with various partners, including both of Helena's brothers. The person I most enjoyed working with was Helena Justina herself Non-judgmental, aware and intelligent, she had understood my approach and my routines pretty well ЈTom the first time I met her. Ever since, she had been my confidante. She would help me chew over ideas, where possible she would accompany me to interviews, she researched backgrounds, worked out timescales, often came up with solutions. Importantly, she took charge of my finances. The best informer in the world is useless if he becomes insolvent. 'Everything all right, sweetheart?' 'We organised ourselves.' Helena managed to combine reproof about the soldiers' sudden arrival with acknowledgement of my good manners in asking. She knew what most husbands were like; she had been married before me, for one thing. So gratitude just took precedence over complaint. 'The legionaries have taken over the ground floor rooms. They made a few complaints at first, but you will have noticed they are all in their quarters now, rather chastened.' I raised my eyebrows but Helena did not bother to elaborate. 'Clemens has complained about the damp; I told him the Tiber floods us every spring and suggested they might like to leave before then…At least we don't have the sewers backing up in our home. I've heard there's a terrible stink three doors down and everyone there has fallen ill.'

'We don't have backing-up shit,' I explained, 'because in all the time he lived here -' which must have been twenty years – 'my skinflint father never paid for a connection to the Cloaca. It looks as though our privy empties into the city sewer system, but I suspect our waste just runs into a big cesspit out back.'

'Well at least there is a cesspit,' Helena replied brightly. 'More cheese, Marcus?'

We ate in silence, thoughtfully. Any minute now we would start talking about my mission. I could see Jacinthus out of the corner of my eye, still staring at us. As he was a slave it was easy to ignore him, but perhaps I'd better not. He was lean and dark, about twenty-five. I had been told by the dealer when I bought him that his previous owner simply wanted a change of face around the house. I did not trust the story. I wondered where Jacinthus originated. Like the majority of slaves, he looked Eastern and not at all German. I supposed I should dig into his background a bit more, if we were to speak freely in front of him. 'You had a visitor this evening, Marcus. A woman called Zosime.' 'From the Temple of Жsculapius? I didn't expect her to seek me out, or I would have briefed you, sweetheart.'