No chance of that. Aelianus was in Greece – and I was about to hear very bad news about what had happened to our missing Justinus. It began when we were greeted on the threshold by Albia, in tears.

'Marcus Didius, something terrible has happened – I've been searching for hours but I can't find the dog anywhere. Nux has run away!'

‘You are joking, Albia? You cannot seriously mean, not only do I have to search for a missing murder suspect, and my missing brother-in-law – but now I must waste yet more time and effort looking for a dog?'

'I cannot go; you do not let me roam outside.' That never stopped her when she wanted to buy cinnamon cakes.

Albia spent a lot of time imagining she was a princess, among whose accessories was a noble hunting hound, a role she crazily assigned to Nux; the little dog just let her get on with it. Albia loved Nux. Nux returned the favour. To the rest of us my pet was a scruffy, often stinky bundle, whose matted, multicoloured fur nobody would willingly investigate closely. Nux was friendly and full of life, but she had no pedigree. She had adopted me. She came from the streets and saw me as a soft touch. She was right, too. Nobody who had a choice would let Nux into their home. I took in the dog, and later I took in Albia, because their lives at the time were even worse than my own. Besides, in both cases, I blamed Helena. She wanted to believe she was in love with a generous person, a benefactor of the oppressed. She had willed me to do it. Both times. 'Poor Nuxie was upset when the soldiers came, Marcus Didius.' 'Have the bastards mistreated her?' 'No, but she doesn't understand why they are all in her house.' 'She'll come home of her own accord.' 'How can you be so heartless? The streets are wild with revellers – she will be terrified!'

Infected by Albia's agitation, both my children began wailing. Julia and Favonia, two fine little tragic actresses, were clutching Nux's favourite toys and looking piteous. Needless to say, I soon found myself promising to go out and find the lost doggie. Trusting young faces beamed at heroic Papa, expecting miracles. Albia came with me. I think she suspected I would bunk off to a wine bar. (No, sweetheart; that was last night.) Eventually, when we had walked all the local streets and alleys, feeling like fools as we called the dog's name, I got sick of being jumped at by revellers in fancy dress who then ran off whooping. I marched to the vigiles' patrol house, and asked to see Petronius. Albia stuck with me, glaring balefully.

'Petro – I want you to tell the men to look out for my dog, please. Don't say anything!'

Petronius Longus eyed up the situation; saw I was being supervised; saw that this was not my own idea. He revelled in my discomfiture. 'You mean, Falco, my hard-pressed lads are to ignore all the arsonists, plotters, market-trashers, temple-defilers, robbers, rapists and heartless killers -' 'I said, don't say anything.' 'What – not even, I hope you've come to collect your dog?'

Nux had been recaptured by Petronius himself. He had spotted her slinking up an alley, covered with mud and worse. Fortunately the vigiles keep a plentiful cache of water. Now washed and fluffed up prettily, my dog had established herself as a guest in the all-night galley that kept the men supplied with hot rissoles and mulsum. She had her snout in a bowl of delightfully rich broth and did not want to come home. She wagged her pert tail when she saw us. Nux did not believe in guilt.

'Oh you naughty girl; they've been spoiling you!' Albia was entranced.

None of Petro's cohort were likely to pass up the chance of showing a bright young woman around the excubitorium, their local outstation here in the Thirteenth District, so I had to wait with the dog while pumping engines sprayed water all over the yard and long ladders were rushed to imaginary blazes; then even the cells were opened up so Albia could look in wide-eyed at that evening's bunch of really stupid drunks who had thrown nuts at the watch. While I waited, lolling in the doorway of Petro's office so I could keep an eye on Albia and prevent any malpractice, Petro took delight in telling me there had been no progress in the surreptitious search for Veleda. 'Your trail is cold, Falco.' I thanked him courteously.

The lads had led my foster-daughter into the depths of their equipment store, so I had to saunter over there. Of course they would be stupid to try anything on with her – but in their eyes, once presented with the opportunity, they would be stupid not to try. They were all ex-slaves, all with a hard attitude; they needed it to do their job. Left to themselves, they would have my teenager bemused on a pile of esparto mats in ten minutes, wooing her with a private demonstration of their ropes and fire axes – then luring her into other things. Albia could look after herself. Still, best to avoid that situation. If the alarm sounded, we did not want half the duty fire response group to be doubled up in pain after a kneeing from a lass who was far more streetwise than she looked.

I gave the girl the wink that it was time to go. Always alert, she took the hint, thanked the men sweetly, and came with me. We had crossed the yard, waving to Petronius, who saluted us satirically. As we approached the big double-gated exit, Fusculus came in. He was Petro's best officer, increasingly rotund, cheery and totally imperturbable. 'I0, Fusculus! How goes it with the king of nipping and foisting?' Fusculus loved lore and cant. If a criminal activity lacked technical terms to describe it, he would invent some.

Now he squinted at me, unsure whether these were real variations he ought to know; his eyes showed suspicion, though he rallied fast. 'All posy-posy on the Via Derelicta, Falco.' While Albia stared in puzzlement, I let him chatter happily. 'Is that dog yours? She's a ferrikin!'

'Right up there with the champions of fragonage,' I agreed. I was so glad to have found Nux so easily, I had stopped being sour. The way my mission was going, to have found any missing person, even a lost pet, was a bonus.

'A woozIer,' nodded Fusculus approvingly. I think that was one of his coinages. But you never knew with this dictionary dabbler. Canine woozling could be traditional among totters' lurchers. Romulus might have owned a woozIer, queen among beasts around the antique shepherds' folds… No, probably not. I bet my Nux was scared stiff of wolves. '- I'm glad I've seen you, Falco.' 'I'm honoured to bring joy to you, my dear Fusculus.' He went with the joke. 'It's a pleasure to be in the company of a civilised man. Top-pigeonhole in life's columbarium -' Eventually even Fusculus grew tired of playing weird man's bluff 'Dear gods, I do maunder on, don't I? What a wonk.' I raised my eyebrows as if in great surprise. His friendly face wrinkled with fun, then sobered. He was, despite the soft-sponge impression, a rather good vigiles officer. Astute and with an eye for detail. Good in a fight too. Petronius Longus knew how to pick them. 'I gather you're searching for somebody, Falco?' 'Apart from the lost dog? – Nasty but handsome barbarian lady. I believe, with a very bad headache.' 'Oh don't give up! You can work your charm on her.' Albia shot me a sharp sideways glance. Fusculus carried on blithely, as if unaware of the damage he had just done to my domestic reputation. He knew all right. 'But I don't mean the priestly pullet.'

'There's Justinus too; you know him. We work together. He's missing. My brother-in-law, the mild one.'

'Well, I'm glad it's not the vicious one.' This time Albia bridled; she seemed to have a latent admiration for Aelianus. Not all that latent sometimes. When they were together they tended to gang up like starlings. 'No, Aulus is in Greece. I've only one of them to worry about. He hasn't been seen for two days now.' Fusculus now lowered his voice. 'I've just come from a recce. Heard word of a possible.' I stiffened. 'Straight stuff?' 'Partially reliable. Seventh Cohort.' I fumbled to recall the cohort delegations. 'Seventh – that's the Fourteenth district and… the Ninth?'