Maia was gone a long time. I went out in yesterday's tunic anyway.

My first task was to check with the Censor the date of Helena's divorce. The record office was closed because it was a public holiday, a frequent menace in Rome. I knew the watchman, who was used to me turning up out of hours; he let me in by the side entrance for his usual modest fee.

The document I wanted must have been deposited early last year, because afterwards Helena had gone to Britain to forget about her failed marriage, which was where she met me. Knowing that, I found the paperwork in an hour. My wild stab had been unerringly accurate: Helena Justina had shed her husband eighteen months ago. If Pertinax wanted her to marry him within the time limit for inheritance, he had just three days left.

Next I walked around the Aventine, hunting for the man who might identify the big iron key I found hidden in that chest. This was my own sector, though among one-man byways where I rarely went. Eventually I bumped round a corner where some slack-mannered basket weaver had piled giant hampers and panniers all over the pavement, lethal to passers-by. I stubbed my toe on the kerb while I was looking out for the antisocial caneware, then came across a fountain where a river god was contemplating the sad rivulets that trickled from his navel as morosely as he had been three months before. Kneeling in the lichen, I scooped up a drink then started banging on doors.

When I found the right apartment, its burly, black-bearded occupant was at home, relaxing after lunch.

'I'm Didius Falco. We met once…' He did remember me. 'I'm going to show you something. I want to know where it belongs. But only tell me if you feel sure enough to repeat it in a court of law.'

I produced the iron key. The man held it in one hand and gave due consideration before he spoke. It was nothing special: the straight sort, with a large oval handloop and three plain teeth of even lengths. But my potential witness ran his forefinger over a faintly scratched letter 'H' which I had noticed myself on the widest part of the stem. Then he looked up, with those deep, dark, beautiful oriental eyes.

'Yes,' said the priest of the Little Temple of Hercules Gaditanus sadly. 'That is our missing Temple key.'

At last: hard evidence.

Seeing the priest wiping off his beard with a dinner napkin reminded me I was short of sustenance myself. I had a bite in a cookshop, then strolled along the river walk, thinking about my discoveries. By the time I returned to Maia's house I was more optimistic.

Maia had been to Lenia's, come home for lunch, then vanished to visit my mother, but she had left a bundle of my garments, most of which I recognized dismally; these were all the tunics I had never bothered to pick up from the laundry because they had sleeves unstitched or lamp-oil burns. The most decent was the one I had worn when I disposed of the warehouse corpse. I had dumped it on Lenia afterwards, where it had been waiting to be paid for ever since.

I sniffed at it, then pulled myself into the tunic, and was pondering my next move against Pertinax when Maia came home.

'Thanks for the clothes! Was there any change?'

'Comedian! By the way, Lenia said somebody keeps trying to find you-and since the message is from a woman, about an assignation, you may want to know-'

'Sounds promising!' I grinned cautiously.

'Lenia said…' Maia, who was a pedantic messenger, prepared a faithful recitation. '"Will you meet Helena Justina at the house on the Quirinal because she has agreed to talk to her husband and wants to meet you there?" Are you working on a divorce?'

'No such luck,' I said, with foreboding. 'When am I to go?'

'That could be a snag-the servant mentioned this morning. I would have told you at lunchtime, but you weren't here-'

I spat a short exclamation, then shot from my sister's house without waiting to kiss her, thank her for yesterday's custard, or even explain.

The Quirinal Mount where Pertinax and Helena had lived when they were married was unfashionable, though people who rented apartments in this pleasant, airy district were rarely doing so badly as they complained. While Vespasian was still a junior politician his youngest child Domitian, the scorpion's sting in the Emperor's success, had been born in a back bedroom in Pomegranate Street; later the Flavian family mansion had been there before they fixed up a palace for themselves.

I felt odd, coming back to the place where I had worked thinking Pertinax was dead. Odd, too, that Helena regarded her old home as neutral ground.

Since our house clearance, the building itself remained unsold. It was what Geminus would call a property 'waiting for the right client'. By which he meant, too big, too expensive, and with a nasty reputation for harbouring ghosts.

How true.

There was a porter from the Palace payroll whom I had installed to guard the mansion until its freehold was transferred. I expected him to be fast asleep at the back of the house, but he answered my urgent banging almost at once. My heart fell: that probably meant he had been roused from his normal slumbers by previous activity today.

'Falco!'

'Has a man called Pertinax been?'

'I knew he was trouble! He claimed to be a buyer-'

'O Jupiter! I told you to keep out passing speculators-is he still here?'

'No, Falco-'

'When was it?'

'Hours ago-'

'With a lady?'

'Came separately-'

'Just tell me she didn't leave with Pertinax.'

'No, Falco…'

I squatted on the porter's stool, held my temples until my temper cooled, then made him go calmly through what had occurred.

First Pertinax himself had conned admission. He started walking round quietly, just like a prospective purchaser, so since there was nothing to steal the porter left him to it. Then Helena arrived. She asked after me, but came in without waiting.

At that point she and Pertinax seemed like a couple-probably, the porter deduced, virtual strangers whose marriage their relations had recently arranged. They walked upstairs, where the porter heard them arguing-nothing out of the ordinary when two people view a house: one always loves the outlook while the other hates the amenities. My man kept his head down, until he heard voices more sharply raised. He found Helena Justina in the atrium, looking badly shaken, while Pertinax was bellowing at her from the landing above. She ran out straight past the porter. Pertinax rushed after her, but at the street door he changed his mind.

'Did he see something?'

'The lady was talking to a senator outside. The senator could see she was upset; he helped her into her chair, urging the bearers to hurry-'

'Did he go with her?'

'Yes. Pertinax hung in the doorway, muttering, until he saw them leave together, then he made off too-'

My first thought was that the senator must have been Helena's father, but I learned differently almost at once. Violent knocks announced Milo, the dog-taming steward.

'Falco-at last!' Milo gasped, out of breath despite his fitness. 'I've been looking for you everywhere-Gordianus wants you at our house urgently-'

We wheeled out of the Pertinax house. Gordianus also had a mansion on the Quirinal; on the way Milo told me that the Chief Priest had brought himself to Rome, still out for vengeance from his brother's murderer. Since the Quirinal was such a respectable district, after last night's sticky heat Gordianus had risked an unattended morning stroll. He had spotted Pertinax; followed him; watched Helena arrive; then saw her rush out. All Milo could tell me was that immediately afterwards Gordianus himself took her home.