I had sent one of the soldiers to tell Petro I was home, and ask him about the situation in the city. He whizzed straight around to our house. I should have remembered he rarely worked in the day so would be free to socialise. Anyone would think the bounder knew he would walk in on me just as I sat down for a private interrogation of the priestess. Petronius had a black eye. 'What happened to you?' 'Forgot to duck. Pelted with a festive nut.' 'Some street urchin?' 'No, Maia.' Petronius Longus took one look at Veleda and announced that she was too gorgeous for me, so he had better stay to lunch. Since it was only mid-morning, that put an end to any hopes I had of a session alone with her. Alone apart from Nux, that is; for the dog was lying asleep at my feet, re-establishing her rights after my two days away from home; she treated the forest femme fatale as if she wasn't there. Helena had had to go shopping, urgently needing to replenish the store cupboard, which the soldiers had emptied while we were away. Albia was helping Galene keep the children quiet. The legionaries had been posted on protective guard around the house and on the roof terrace.

Hoarse with curiosity, Petro assured me I would be safer having a witness if I was prying into state secrets. The priestess gazed at my brazen old tentmate as if he was the kind of tree-trunk snail her tribe ate mashed up on crusts at feasts. He had not changed since we were lads; female disdain only encouraged him. 'Falco's all right,' Petronius confided with his friendliest manner. 'But a famous lady deserves respect; you need an interview with a professional.' 'Lucius Petronius Longus lives with my sister,' I warned Veleda. 'The suspicious, hot-headed one.' 'Are you related to everyone in Rome, Falco?' 'It's the only way to be in this city.' Petronius sprawled in Helena's armchair, and happily beamed at both of us. I tried to put him off by abandoning my interview and grilling him on why the mood on the streets had seemed so angry last night. Petro told me that Anacrites had caused the dismay. In a wayward ploy that was typical, the Spy had openly let it be known that Rome's loathed and feared enemy was a fugitive at large – making sure he included the detail that she had taken flight after horrifically murdering one of her aristocratic Roman hosts. He was now leaving it to the mob to turn up her hiding place and hand her over.

'Or tear her to pieces, of course,' Petro suggested. 'Oh sorry, sweetheart!' Veleda produced a wan smile. She had passed beyond insults.

Anacrites had seen fit to offer a reward, though given the constraints of his budget, it was a ludicrously small one. However, it had made partying in the streets assume a violent trend. To enhance the air of menace, the Praetorian Guard were openly conducting a stop-and-search of any unaccompanied women; ugly stories had circulated about how they did it. Anybody German, or with German connections, had left town if they knew what was good for them. Foreigners of all flavours were hiding indoors; naturally there were some who had not been told about the problem, had not understood the implications, or just did not speak the right language to grasp the danger to them. Many had discovered the situation when they had been beaten up by 'patriotic Romans' – most of whom were foreigners by birth, of course. The people who were keenest to look patriotic were the ones who originated in Upper and Lower Germany.

Petronius cursed this development. He said the vigiles already had their hands full, without beatings on every street corner. Saturnalia meant a big increase in fires, due to the enormous number of festive lamps in feckless homes. There were fights everywhere, arising from friends and family fall-outs, even before this new rash of anti-barbarian feeling. Petro was glad that the vigiles could at least stop the searches he had set in hand for me; I asked him to tell the cohort commanders this was because of poor results, without mentioning that I had in fact found Veleda. I wanted to avoid bounty hunters turning up at my house. 'Quite right!' exclaimed Petronius, managing to imply I was a bounty hunter myself Still seeking to distract him, I asked if the vigiles searchers had come across anything unusual to do with dead vagrants. He gave me a sideways look, but slowly admitted there might be a problem. 'We have been aware of an increased unclaimed-corpse count for some time.' 'Does Scythax know about it? Or is he somehow mixed up in it?' 'Of course not. Crazy suggestion, Falco.' 'Hear my words: he had a very fresh cadaver of a runaway slave laid out on his workbench when we took in Lentullus. According to Scythax, someone dumps them outside the patrol house, but that story sounds fishy.' 'Reminds me: my tribune wants you to shift Lentullus off our premises. ' 'Tell Rubella to stuff a festive garland where it hurts. And answer my question, please.'

Petronius shrugged and admitted there had always been a high death rate among the homeless, as long as he had been in the vigiles. Recently numbers had increased; they blamed the winter weather. 'So why does your doctor involve himself?' Petro looked shifty, so I kept probing until he stopped wriggling and owned up feebly, 'Scythax takes an interest in why the vagrants die.' 'An interest – how?' 'I believe,' said Petronius, looking shy, 'he has been known to dissect the corpses.' I presumed that information had to be kept confidential. 'Using the dead for autopsies is illegal, I'm told.' 'Too right, it is! We don't want unnatural practices in backstreet morgues. ' 'No, much better to have them right in your patrol house!'

On my promise of discretion, Petronius said what I already knew, that Scythax was occasionally allowed to take away the corpses of criminals who died in the arena – so long as he carried out any scientific research in his spare time and it was all kept quiet. The excuse was that what Scythax learned could help the army repair wounded soldiers. In any case, post-mortems only happened when the executed criminals had no family to complain, and when Scythax could pay enough bribes to sweeten the arena staff.

'So when his supply from the arena dwindles, he encourages the dumping of dead runaways on your doorstep. Does he advertise this service? Jupiter, Petro, does he buy the bodies? And if so – you need to think about this – is somebody killing off vagrants deliberately for Scythax?' Petronius Longus sat bolt upright. 'Nuts, Falco. Scythax would never countenance that. Besides, there are far too many runaway slaves being found dead!' 'So it's really a problem? You think you have a serial killer?' 'I think it's possible.' 'Because the targets are vagrants, does nobody care?' 'I care, Marcus.' All this time, Veleda had been sitting quiet, listening to us pretty blank-faced. She had a basket chair, like the one Petronius had commandeered, and was wrapped in shawls, with her feet on a small footstool. Had she had a wool basket at her feet, a child on her chair arm and a pet bird in her lap, she could have been a classic Roman matron. You might say she was too blonde – but a lot of married women I knew had turned mysteriously golden-haired, once they got their hands on their husband's income.

The intent way she was listening to us had attracted my attention. I doubted she was merely entranced by our talented oratory. 'Veleda, you went out on the medication run from the Temple of Жsculapius. They find a lot of these bodies. Anything you can tell us about it?'

'Did she?' exploded Petronius. Assuming he was upset at the thought of her wandering loose on the streets that his cohort patrolled, I ignored him. 'I never saw anything like that.' Veleda disappointed me. Even if she had seen something, gratitude to the temple kept her silent. I decided it was time to pick up my original intention and tackle her about the death of Scaeva. Petronius Longus crossed his booted feet on a low table, linked his hands behind his head, and watched me proceed. His stare was supposed to unnerve me. I had known him a long time and just ignored his attitude.