I was feeling sour. An intellectual diet of The Girl from Andros, followed by The Girl from Santos, then The Girl from Perinthos, had not produced a sunny temperament. This turgid stuff might appeal to the kind of bachelor whose pick-up line is asking a girl where she comes from, but I had moved on from that two years ago when a certain girl from Rome decided to pick me up.

Helena smiled gently. She always knew what I was thinking. 'Well that's the men. There's no particularly striking motive there. So maybe the killer we heard was acting for somebody else. Shall we reconsider the women?'

'I'll always consider women!'

'Be serious.'

'Oh I was: Well, we've thought about Phrygia.' I stretched luxuriantly. 'That leaves the eavesdropping maid.'

'Trust you to spot the beauty at the bar counter!' Helena retorted. It was hardly my fault. Even for a bachelor who had had to stop asking strange women where they hailed from, this beauty was unmissable.

Her name was Byrria. Byrria was genuinely young. She had looks that would withstand the closest inspection, a perfect skin, a figure worth grabbing, a gentle nature, huge, glorious eyes:

'Perhaps Byrria wanted Heliodorus to give her some better lines?' wondered Helena far from rhapsodically.

'If Byrria needs anyone murdered, it's obviously Phrygia. That would secure her the good parts.'

I knew from my reading that in plays which could barely support one good female role, Byrria must be lucky to find herself a speaking part. Such meat as there was would be snaffled by Phrygia, while the young beauty could only watch yearningly. Phrygia was the stage manager's wife so the chief parts were hers by right, but we all knew who should be the female lead. There was no justice.

'In view of the way all you men are staring,' said my beloved icily, 'I shouldn't wonder if Phrygia would like Byrria removed!'

I was still searching for a motive for the playwright's death – though had I known just how long it would take me to find it I should have given up on the spot.

'Byrria didn't kill Heliodorus, but good looks like hers could well have stirred up strong feelings among the men, and then who knows?'

'I dare say you will be investigating Byrria closely,' said Helena.

I ignored the jibe. 'Do you think Byrria could have been after the scribe?'

'Unlikely!' scoffed Helena. 'Not if Heliodorus was as disgusting as everyone says. Anyway, your wondrous Byrria could take her pick of the pomegranates without fingering him. But why don't you ask her?'

'I'll do that.'

'I'm sure you will!'

I was not in the mood for a squabble. We had taken the discussion as far as we could, so I decided to abandon sleuthing and settled down on my back for a snooze.

Helena, who had polite manners, remembered our Nabataean priest. He had been sitting with us contributing total silence – his usual routine. Perhaps restraint was part of his religion; it would have been a tough discipline for me. 'Musa, you saw the murderer come down the mountain. Is there anybody in this group of travellers whom you recognise?'

She did not know I had already asked him, though she ought to have guessed. Musa answered her courteously anyway. 'He wore a hat, lady.'

'We shall have to look out for it,' replied Helena with some gravity.

I grinned at him, struck by a wicked possibility. 'If we can't solve this puzzle, we could set a trap. We could let it be known that Musa saw the murderer, hint that Musa was planning to identify him formally, then you and I could sit behind a rock, Helena, and we could see who comes – hatted or hatless – to shut Musa up.'

Musa received the suggestion as calmly as ever, with neither fear nor enthusiasm.

A few minutes later somebody did come, but it was only the company bill-poster.

Helena and I exchanged a surreptitious glance. We had forgotten this one. He had been in Petra and ought to have been included in our list of suspects. Something told us that being forgotten was his permanent role. Being constantly overlooked could give him a motive for anything. But maybe he accepted it. So often it is the people who have who think they deserve more. Those who lack expect nothing else from life.

Such was our visitor – a miserable specimen. He had appeared around a corner of our tent very quietly. He could have been lurking about for ages. I wondered how much he had overheard.

'Hello there! Come and join us. Didn't Chremes mention to me that your name is Congrio?'

Congrio had a light skin covered with freckles, thin straight hair, and a fearful look. He had never been tall to begin with, and his slight, weedy body stooped under burdens of inadequacy. Everything about him spoke of leading a poor life. If he was not a slave now he probably had been at some stage, and whatever existence he snatched for himself these days could not be much better. Being a menial among people who have no regular income is worse than captivity on a rich landowner's farm. No one here cared whether Congrio ate or starved; he was nobody's asset, so nobody's loss if he suffered.

He shuffled near, the kind of mournful maggot who makes you feel crass if you ignore him or patronising if you try to be sociable.

'You chalk up the advertisements, don't you? I'm Falco, the new jobbing playwright. I'm looking out for people who can read and write in case I need help with my adaptations.'. 'I can't write,' Congrio told me abruptly. 'Chremes gives me a wax tablet; I just copy it.'

'Do you act in the plays?'

'No. But I can dream!' he added defiantly, apparently not without a sense of self-mockery.

Helena smiled at him. 'What can we do for you?'

'Grumio and Tranio have come back from the city with a wineskin. They told me to ask whether you wanted to join them.' He was addressing me.

I was ready for bed, but put on my interested face. 'Sounds as if a sociable evening could be had here?'

'Only if you want to keep the caravanserai awake all night and feel like death tomorrow,' Congrio advised frankly.

Helena shot me a look that said she wondered how the town-and-country twins could tell so easily who was the degenerate in our party. But I did not need her permission -or at least not when this offered a good excuse to ask questions about Heliodorus – so off I went to disgrace myself. Musa stayed with Helena. I had never bothered to ask him, but I deduced that our Nabataean shadow was no drinking man.

Congrio seemed to be heading the same way as me, but then turned off on his own. 'Don't you want a drink?' I called after him.

'Not with that pair!' he responded, vanishing behind a waggon.

On the surface he spoke like a man who had better taste in friends, but I noticed a violent undertone. The easy explanation was that they pushed him around. But there could be more to it. I would have to scrutinise this bill-poster.

Feeling thoughtful, I made my own way to the Twins' tent.