We men were in white. We started in togas, though we soon flung them off. Helena's father had his fond, faintly cautious expression. Her brother Aelianus boasted a scowl and a Spanish belt. I had been smartened up until I felt like a whole guild of shoemakers on their big day out.

Justinus had failed to appear that night. Everyone knew he must be mooning around Pompey's Theatre. `He won't forget,' his mother assured us as she led us indoors. He might. (The actress might be exceptional, and she might choose tonight to notice him.) Helena and I gulped, then prayed for him.

While the women rushed away to share urgent news, I was led off for a pre-dinner winecup with the Senator (honeyed mulsum, strictly traditional; makes you feel sick without letting you get drunk). Camillus Verus was shrewd and intelligent, with a diffident manner. He did what was necessary, and didn't waste effort on the rest. I liked him. It mattered to me that he should be able to tolerate me. At least he knew the strength of my feelings for Helena.

The Camillus family were certainly patrician when viewed from my own perspective, though there were no consuls or generals in their ancestry. They were rich – though their wealth was in land and my father probably owned far more portable collateral. Their house was spacious and detached, a lived-in town villa with water and drainage but rather tired decor. Lacking expensive works of art, they relied on old-fashioned features for domestic tranquillity.

Tonight the courtyard fountains were splashing merrily, but we needed more than that to cool the air as the Senator introduced me to his elder son.

Aelianus was two years younger than Helena, two years older than Justinus. He looked much like his father – sprouting straight hair and slightly stooped shoulders. More chunky than Justinus and Helena and heavier-featured, he was less good-looking as a result. His abysmal manners were a patrician cliche. Luckily I had never expected a senator's son to approve of me. That was fine; it let me off trying to like him.

`So you're the man who's been pushing my young brother's career along!' exclaimed Aelianus.

Nearly a decade his senior, and worth ten times more in useful qualities, I refused to agitate myself. `Quintus has a warm personality and a fine intellect. People like him, and he's interested in everything – naturally such a man stands no chance in public life! Unlike you, I'm sure.' Well done, Falco; an insult, but nicely ambiguous.

Young Justinus stood every chance; in fact. But I don't stir up trouble; close relatives can usually find enough things to be jealous about.

`And did you get him interested in the theatre too?' his brother sneered.

It was the Senator himself who said, `He selects his own hobbies – like all of you.' That had to be a fatherly dig; I sat back and wondered what dubious activities the pious Aelianus liked. If he gave me any trouble, this would be something to find out.

`Let's hope my brother's hobby doesn't last or my sister's either!'

There were now so many stars alongside Justinus' name on the army list, a scandal might just make him appear more intriguing to the public. I refrained from saying that. Aelianus had completed his own military service rather dully, then a year as a governor's unpaid aide-de-camp in Baetica had failed to give him lustre. On the other hand, none of that had been his own fault. Luck stepped around me pretty smartly too, so I said kindly, `Don't be jealous. Your brother was just in the right province, at the right time.'

`And of course he knew you!'

Again there was an unpleasant scornful, note. Aelianus was naive enough to expect me to flare up. Instead his father said mildly, `That was indeed fortunate. When Marcus was sent on one of his peculiarly demanding missions, your brother was able to join him.'

`Did you approve of that?' Aelianus demanded accusingly. `I've heard what Justinus got up to in Germany was damned dangerous.'

`I didn't know until it was over,' Camillus replied honestly.

The young man was bursting with outraged dignity. `There are things we ought to get straight.' The Senator and I glanced at one another then let him get on with it. He needed to make a racket. That was easier than arguing. `This man is a common informer.' I noticed he found it impossible to use even my formal name. `The situation with my sister is damaging our family.' He meant that it might reflect on his own career.

The Senator looked annoyed. Whatever he thought about his finely bred daughter absconding with a piece of rough cheese, he always put the best face on it. `Falco is an imperial agent. He has the confidence of the Emperor.'

`But Vespasian hates informers.'

I laughed. `Except when he needs them.'

The younger Camillus was still sounding off pompously. `I have seen no public recognition of the role of "imperial agent". It carries not official title or salary. And as I understand it, although there was once talk of a substantial reward, it has failed to materialise!'

I made an effort to avoid reacting. I had promised Helena not to involve myself in conversations that might end with my fist shattering her brother's jaw.

Camillus Senior looked embarrassed. 'Falco's work is necessarily secret. Don't be offensive to our guest.' He tried gamely to change the subject: `You look in good form, Marcus. Travel suits you.'

`You should see me in my Palmyrene trousers and embroidered hat…' I sighed. Chitchat on Oriental matters would dodge the problem but not solve it. `Your son is quite right, Senator. I was promised social advancement, and it has been refused.'

Camillus must have heard about it from Helena. As a member of the Establishment he seemed to feel personally responsible. He scratched his nose; light gleamed on a workaday garnet signet ring. `It's a misunderstanding, Marcus. It can be resolved.'

`No, Domitian Caesar gave me a very clear ruling, and when I discussed the matter with Titus last week he was unable to change that.'

`Titus told me,' answered the Senator. `Rulings do tend to become immutable if they involve denying just rewards!' His sense of humour was always refreshingly dry. `Well, tell me if I can help… I gather you're working on the law-and-order issue at present?' So much for keeping the post-Balbinus investigation confidential.

`Yes, I'm on the special commission.'

Camillus noticed my dark mood. `Not enjoying it?'

`Mixed feelings; mixed loyalties.' The conversation had shifted. The Senator and I were talking at a level that now excluded Aelianus. I went back to one aspect of what Camillus had said: `I'm asking myself how much of my personal chat with Titus Caesar he passed on, sir? Has he pre-empted a private discussion I intended to have with you?'

Camillus smiled, waving a hand in acceptance of the fact that he had been told he was to be a grandfather by someone other than me. `I realised Titus was being premature.'

'I'm sorry for it. You know how things work, sir.'

`You had to seize your opportunity,' he agreed. Well, for Helena's sake he would want me to have tried. Our relationship stayed easy. `Are you pleased?' he asked. I let a grin answer him. Then we both stopped looking so delighted, as like dutiful men we both considered the perils to Helena.

'I still think something can be sorted out for you, Marcus.' Vespasian, like any good Roman, had his private clique of friends who advised him; the Senator was one of them, once close, and still consulted. It could be made to work on my behalf if I could accept having strings pulled. The senator knew my feelings about that. `Will you let me speak to the old man?'

`Better not.' I smiled. Even with his personal interest, it was gracious of him to offer. But I had to do this myself. `My new assignment is a complex one. Let's see the results before I call in imperial favours!'