Helena Justina must have let her lunch go down hiding under a tree and listening to us. Now here she came: a tall girl with a bite like Spanish mustard, whose scorn any wise informer could learn to live without. Her face was white as a shell; she had a sharp, withdrawn expression that I remembered from when I first met her, when she was dismally unhappy after her divorce.

'Please don't get up!' Larius and I made a half-hearted attempt to raise our backsides, then fell down again. Helena sat there on the dry grass with us, managing to look rank conscious and remote. 'Who's this, Falco?'

'My sister's son Larius. His mother reckons he needs cheering up.'

She smiled at my nephew in a sweet way she had refused to smile at me. 'Hello, Larius.' She had a direct approach to young people which I could see attracted him. 'Someone should warn you, your uncle's a hypocrite!'

Larius jumped. She gave me an irritating smile. 'Well, Falco leads a dangerous life, of course. In fact one day he'll die of a brain tumour when some furious woman breaks a big stone pot on his head-'

By now Larius was looking seriously alarmed. I jerked my head and he made himself invisible.

It was no business of a senator's daughter to invade the scene when I was trying to do my duty as a substitute father.

'Lady, that was harsh!' I watched as she tore at the grass beside her, breathing furiously again.

'Was it?' She stopped torturing the fescue and turned on me. 'Do private informers come from some barbarian tribe whose gods let them fornicate without the normal risks?' Shocked at her language, I started to speak. 'Your advice to the boy,' she overruled me with some malice, 'was a complete farce!'

'Oh, that's unfair-'

'Wrong, Falco! Sponges in vinegar, Falco? Calfskin scabbards? Holding back manfully?'

I experienced a surge of reminiscence that was embarrassingly physical… 'Helena Justina, what happened between us was-'

'A great mistake, Falco!'

'Well, slightly unexpected-'

'Once!' she scoffed. 'Hardly the second time.'

True.

'I'm sorry-' She heard my apology arching her strong eyebrows in a way that made me furious. I forced myself to ask, 'Is anything wrong?'

'Forget I spoke,' she answered bitterly. 'Rely on me!'

There was nothing safe to say to her, but after a desperate moment I tried anyway: 'I thought you understood, you could rely on me!'

'Oh, for heavens' sake, Falco-' In her usual crisp style Helena abandoned it. 'What have you dragged me all the way out here to say?'

I leaned against a gnarl in the olive tree behind. I felt drugged; starvation perhaps.

'Enjoy your lunch? Larius and I had apples; mine was the one where a maggot had got at all the best bits first.' She was frowning, though probably not because she wished she had brought us a basket of scraps. Seeing a woman looking anxious over my appetite generally makes me relent. 'Don't worry about us… Tell me about Barnabas!'

Immediately the tension between us eased.

'I knew him of course,' Helena said at once. She must have been thinking it over while she had lunch. Her expression flooded with interest. She loved a mystery. And I always felt more cheerful when I had her to help. 'He could easily be here. He and Gnaeus often came here in summer; they kept racehorses on the farm-' It was nothing to do with me, yet it always jarred when she called her vile ex-husband by his personal name. 'What has the fool been up to, Falco? Not really murder?'

'Misguided vengeance campaign, according to the Palace, though I have stronger views! Don't ever approach him; he is much too dangerous.' She nodded: an unexpected treat. I had rarely been able to influence the lady (though that never stopped me giving her advice). 'When you knew him, what was he like?'

'Oh, I hated having him round the house; he seemed to despise me, and I thought that affected my husband's attitude. He had a dreary effect on my marriage. Even at home we never had a meal in private; Barnabas was always there. So he and my husband talked about their horses and pretty well ignored me. They went everywhere together-have you discovered why they were so close?'

'Because they grew up together?'

'It was more than that.'

'Then I don't know.'

She was looking at me so gravely I smiled at her. Once a girl strikes you as attractive, it's difficult to forget. She looked away. I felt the smile fade.

'Barnabas had been born to a female slave on the Pertinax estate; my husband was the legitimate son of the house. They shared one father,' Helena informed me levelly.

Well, it was common enough. A man keeps slaves to serve his physical needs: all of them. Perhaps, unlike Larius, Pertinax senior had lacked an elder relative to educate his habits. More likely, when sleeping with a slave why should he care? A birth only meant one more entry in the plus column of his accounts.

'Is it important?' Helena asked me.

'Well, the facts don't alter-but they certainly make more sense.'

'Yes. There were no other children; these two were tumbled together from infancy. My husband's mother died when he was five; I suspect no one gave him much attention after that.'

'Was there rivalry?'

'Not much. Barnabas, who was older, became very protective and Gnaeus was always ferociously loyal to him-' She poured her story out; she would go on puzzling over it for hours by herself, but she wanted to share it with me.

She stopped. I didn't speak.

She started again. 'They were as close as twins. Castor and Pollux. Little room for anybody else.'

Her mood darkened with an old sadness, regretting her wasted years. Four of them; not so much in the human span. But Helena Justina had gone into that marriage as a dutiful young girl; she had wanted to make it work. Though she finally opted for divorce, I knew her sense of failure had left permanent scars.

'Pertinax was capable of affection, Falco; Barnabas and the Consul were the two people he loved.'

'He was a fool then,' I grated before I could help it. 'There should have been three!'

A ladybird landed on Helena's dress, which gave her an excuse to catch it on her finger and watch it instead of me. The ladybird was prettier anyway.

'I beg your pardon.'

'There's no need,' she said; I could see that there was.

After a short silence she asked me what to do if she found any trace of Barnabas, so I explained how I was staying in Oplontis, and the best time to catch me was in the evenings when we ate. 'It's not far; you could send a slave with a message-'

'Are you staying in Oplontis on your own?'

'Oh, no! Larius and I have a lively female entourage-' She looked up. 'Petronius Longus is here. He has a bevy of little girls.' She had met Petro; she probably thought him respectable (which, in the presence of his wife and children, he generally was).

'Ah, you're with a family! So you're not lonely?'

'It's not my family,' I snapped.

She frowned over that one then started again. 'Are you not enjoying your beach party?'

Defeated by her persistence, I finally sighed. 'You know me and the sea. Sailing on it makes me sick; even staying alongside makes me nervous in case any of my jolly companions suggests a joy ride on the waves… I'm here working.'

'Aufidius Crispus? How far have you got?'

'I've sold a lot of good people new sets of water pipes; hence the dreadful garb.' She made no comment. 'Look, when do you expect I'll hear from you about Barnabas?'

'Today I shall have to let this commotion you've caused settle; tomorrow I had planned going to Nola with my father-in-law.' Helena seemed to hesitate, then she continued. 'Perhaps I can help you with Crispus. I may know people he visits when he comes ashore.'