A tray had been made up with our lunch on it, so I grabbed the tray and carried it to our dining room. Obviously we householders were expected to set an example by eating formally. How formally was a surprise: slices of cold meat had been laid out with military correctness on a serving platter, decorated with neatly halved eggs; each knife was set at a thirty-degree angle on a folded serviette with a bread roll; there were six black olives per person, plus two gherkins; the water jug had been buffed like a lady's hand mirror.

Helena calmed down grudgingly. We found the children. Julia was playing farms with Favonia's little horse-shaped pottery feeding bottle. Favonia was gnawing the leg of a stool. In her own room, our foster-daughter Albia was laughing as she read through a letter; I had no idea who her correspondent was, but if a teenaged girl has a smile on her face instead of the normal filthy scowl, in my view you think yourself lucky and leave well alone. Helena acquired a thoughtful expression, however, rubbing her forehead abstractedly with the back of her hand, like a woman who already has enough to cope with. I grinned reassuringly. As usual, that made her look more anxious. 'Where's the dog?' 'Hiding. Probably in your bed.' Helena and I then assembled with Albia and the children in the dining room, though we did not start to eat. Helena sat silent, and I knew why she was uncomfortable. 'Something is not right here, Marcus.' 'Too perfect. They are taking us for idiots.' 'I'll go -' 'No, leave it to me. I'll deal with it.' 'Oh I love it when you play-act as the father of the family…'

I went back to the kitchen. Nobody heard me coming, so I found them all stretched out on benches, ensconced with mounded bowls of double rations, clearly set in for a siesta they expected to extend all afternoon. A flagon that did not contain water slid its way back on to a shelf and looked innocent, just as I entered. I pretended I had not noticed. Gaudus, for one, was sharp enough to know I had seen it.

'Now look here. In our house we don't have "them and us". I run a benevolent democracy. Our slaves are loved and part of our family; so are army visitors. Helena Justina and I would like to implement a slight adjustment, therefore: Galene and Jacinthus, Gaudus and Scaurus, either you four come and join us decently for lunch, or I'll have to bring the tray right back and the rest of us will come down here.'

Four pairs of hostile eyes stared back at me. I stood my ground and told them to collect cutlery. They knew I was on to them.

I was a Roman. Just as Helena kept the keys to the store-cupboards – which from now on, she really would have to hold in a bunch on her belt – I was the master: father of all the household, priest, judge and king. I would not allow ganging-up in the kitchen. There were damn good reasons for running an establishment the Roman way: it prevented riot and bankruptcy. We all had lunch very pleasantly together as a family. Helena warned me afterwards, we must ensure that none of those four won the bean to be King-for-a-Day at Saturnalia, or they might retaliate with more misrule than we could handle. I returned a genial smile. I was king all the other days. And I myself was determined to allocate that bean.

Helena needed rescuing from domesticity. I told Galene to watch the children, and Albia to watch Galene. Albia agreed readily; she was a born tyrant. We showed Gaudus where the local bakery was; I reckoned that if Galene took him she would be pregnant before the pies coloured in the oven. I was barely coping with ownership of my first generation of slaves; it would be some time before I could face the idea of a dynasty.

I had warned everyone we would be back in half an hour, though we were planning to bunk off for longer. (Next time I would imply I was going out for ages, but then return unexpectedly after ten minutes…)

Suddenly I understood why there were so many suspicious masters. I also understood why they were bad-tempered; I hated the slaves and the soldiers for putting me – a fair-minded, friendly, relaxed character – in that position.

Helena and I stood on the Marble Embankment and slowly inhaled the cool December air like captives drinking in the fresh breath of freedom. Then we set off together on foot for our next enquiry. Always thinking ahead, Helena had persuaded Zosime from the Temple of JEsculapius to give directions for finding Mastarna, the physician Zosime had quarrelled with, who had looked after the young man Gratianus Scaeva until somebody segmented him.

Knowing only that Mastarna lived 'somewhere by the Library of Pollio', it took us a while to identify his house, though I knew that area well and found an apothecary nearby who told us where to go.

‘Presumably you have dealings with him.' I like to find out a few facts in advance.

'Not that one. I always thought Etruscans favoured roots and shoots. You know – gathering herbs by moonlight, pounding bulbs, assembling folklore potions.'

'Mandrake and religious magic?' 'Bloody dogmatist.' The apothecary spat. It was an insult rather than for medical relief 'All he wants are scalpels and saws. I need the ones who prescribe ointments and laxatives. He'll always have idiots with too much money pleading for him to slice bits off them, but how am I to earn a living? Give me a decent empiricist prescribing purges any day. I may as well live near the beast market as across the alley from Mastarna. At least then I could hope the real butchers would give me free oxtails…'

He was still maundering on when we shuffled away and knocked on the doctor's door, keeping our backs to the complaining apothecary in the hope he would not follow us over there. Mastarna was out, but his housekeeper said he would be back soon, and we could wait. She was a short, wide little bundle with her girdle right under her bulging bust, who faced the world with her left shoulder forward, squinting at us with her wall eye. I started to wonder if Mastarna was one of those sinister medical men who collect freaks. He certainly collected fees. He lived in a small but beautifully decorated apartment on the good side of a quiet street. He possessed much desirable furniture, which meant he earned more than I did. His whole house reeked of terebinth resin, however; I thought ours, always smelling of young children, rosemary hair-wash and grilled meats, was healthier.

When he came home, he was impeccably groomed and elegantly turned out. All I knew of Etruscans was that my own nose, which plumb-bobbed straight down from my forehead with no bumps, was reckoned to show that Etruscans had lurked in the Didius pedigree somewhere about the time of the last Carthaginian war. From tomb portraits that had passed through my father's none-too-legitimate auctions, I had gleaned a picture of reclining men and women in rather Greek poses, with slanted eyes and cheerful smiles. Mastarna had none of that strange pointy-eared elfin look. He was as wrinkled as a roof gargoyle. When I asked, he said he came from Forum Clodii, but he looked more Roman than I did and sounded like a swanky lawyer lying his head off over some writ in the Basilica. His tunic was pristine and he wore a toga over it. The toga was meticulously pleated; he was so pleased with the effect, he kept it on at home, and it stayed on even after he learned we were not prospective patients who would need to be impressed. He had a goatee beard. That pigeonholed him for me. The apothecary had been right to curse him. 'It is so good of you to see us without an appointment. I hope you don't mind us calling.' I let Helena do the softening up. Before I could interrogate him fairly, I needed to get over my irritation with his beard. 'Didius Falco is investigating the disappearance of Veleda – we can mention her openly to you, since I believe you knew she was staying at the Quadrumatus house. Inevitably, in view of the timing, my husband has to consider the sad death of your late patient.'