It was too hot, and we were too ill-tempered to sleep. Instead we all sat cross-legged and talked restlessly.

'I feel depressed,' Helena exclaimed. 'We're running out of cities but not solving anything. What are the places we have left to visit? Just Capitolias, Canatha, and Damascus.' She was in a brisk mood again, answering her own questions as if she expected Musa and me to stare into space lethargically. We did that for a while, not deliberately intending to annoy her but because it seemed natural.

'Damascus is big,' I offered eventually. 'There seems a good hope of finding Sophrona.'

'But what if she was at Dium?'

'Then she's probably caught the plague. Thalia wouldn't want her back.'

'Meanwhile we go on searching for her, though, Marcus.' Helena hated wasted effort. I was an informer; I was used to it.

'We have to do something, fruit. We're trapped at the ends of the Empire, and we need to earn our keep. Look, we'll go to the last three cities with the company and if Sophrona doesn't turn up then we'll know we should have tried Dium. If it happens, we can decide what we think about this plague.'

It was one of those moments that hit travellers, a moment when I reckoned our decision would be to take a fast ship home. I didn't say it, because we were both so frustrated and gloomy that even mentioning a retreat would have had us packing our bags that minute. These moods pass. If they don't, then you can suggest going home.

'Maybe there was nothing really wrong at Dium,' Helena fretted. 'We only have the word of a caravan we met. The men who told us may have been lying for some reason. Or it could be no more than one child with spots. People panic too easily.'

I tried myself not to sound panicky. 'Risking our own lives would be stupid – and I'm not going to be responsible for extracting a runaway musician from Dium if taking her to Rome might bring an epidemic there. It's too high a price for a water-organ fugue, however brilliant a player she is.'

'All right.' After a moment Helena added, 'I hate you when you're sensible.'

'The caravanners looked pretty grim when they waved us away,' I insisted.

'I said, all right!'

I saw Musa smile faintly. As usual he was sitting there saying nothing. It was the kind of irritating day when I could easily have lost my temper with him for this silence, so I covered by taking charge: 'Maybe we need to take stock.' If I thought this would perk up my companions, I was disappointed. They both remained listless and glum. Still, I pressed on: 'Looking for Sophrona may be pointless, I agree. I know the girl could be anywhere by now. We're not even certain she ever left Italy.' This was verging on too much pessimism. 'All we can do is to be as thorough as possible. Sometimes these jobs are impossible. Or you may run across a piece of luck and solve the case after all.'

Helena and Musa looked as impressed as a desert vulture who had flown down to an intriguing carcase only to find it was a piece of old tunic blowing against a broken amphora. I try to stay cheerful. However, I gave up on the girl musician. We had been looking for her for too long. She had ceased to seem real. Our interest in the creature had waned, along with any chances we had ever had of finding her out here.

Suddenly Helena rallied. 'So what about the murderer?'

Once again I tried to liven us up with a review of the facts. 'Well what do we know? He's a man, one who can whistle, who must be fairly strong, who wears a hat sometimes -'

'His nerve holds,' contributed Musa. 'He has been with us for weeks. He knows we are looking for him, yet he makes no mistake.'

'Yes, he's confident – although he does jump sometimes. He panicked and tried to put you out of action, Musa, then he soon silenced Ione.'

'He's ruthless,' said Helena. 'And also persuasive: he did make both Heliodorus and Ione agree to go somewhere alone with him. Ione even suspected he was a killer, though I presume that didn't apply in the playwright's case.'

'Let's think about Petra again,' I suggested. 'The chief players went there and came back without the playwright. What have we found out about them? Who hated Heliodorus enough to turn his walk into a swim?'

'Most of them.' Helena ticked them off on her fingers: 'Chremes and Phrygia, because he plagued them about their unhappy marriage and Phrygia's lost baby. Philocrates because they were unsuccessful rivals for Byrria. Byrria, too, because he tried to rape her. Davos partly because of his loyalty to Phrygia, but also because he thought the man was:' She hesitated.

'A shit,' I supplied.

'Worse: a bad writer!' We all grinned briefly, then Helena carried on. 'Congrio loathed Heliodorus because he was bullied, but Congrio is let off because he can't whistle.'

'We'd better check that,' I said.

'I asked Chremes,' she whipped back crisply. 'As for the Twins, they have told us they disliked Heliodorus. But do they have a particular reason? A strong enough motive to kill him?'

I agreed: 'If there was one, we haven't unearthed it yet. They told me that Heliodorus couldn't succeed in doing them down on the stage. If he tried to write poor parts, they could improvise. Well, we know that's true.'

'So they were not in his power,' Helena mused. 'Yet they do say they despised him.'

'Right. And if we come forward in time, one at least -Tranio -has an unsatisfactory alibi for the night Ione died. Everyone else seems to be accounted for that night. Poor Congrio was running around Gerasa writing wrongly spelt playbills. Grumio was joking his heart out in the street. Chremes, Davos and Philocrates were all dining together – '

'Apart from when Philocrates says he left to bed his cheese-maker,' scowled Helena. She seemed to have developed an antipathy for her admirer.

I grinned. 'He showed me the cheese!'

Musa openly chortled too. 'I think the handsome one is too busy to find time for killing people.'

'Eating cheese!' I laughed abusively.

Helena stayed serious: 'He could have acquired the cheese at any time – '

'So long as the shop had a low counter!'

'Oh shut up, Marcus!'

'Right.' I pulled myself together. 'Everyone has an alibi except Tranio. Tranio ducks out by claiming he was with Afrania; I don't believe him though.'

'So we really suspect Tranio?' said Helena, pushing for a decision.

I still felt uneasy. 'There's a worrying lack of evidence. Musa, could Tranio be your whistling man?'

'Oh yes.' He too was troubled though. 'But the night I was pushed off the embankment at Bostra – ' If I ever forgot that incident, Musa never did. He thought about it again now, cautious as ever. 'That night, I am sure Tranio was walking up ahead of me. Congrio, Grumio, Davos – they were all behind. It could have been any one of them, but not Tranio.'

'You're quite certain?'

'Oh yes.'

'When I asked you about it straight after the incident -'

'I have thought about it a lot more since. Tranio was in front.'

I considered this. 'Are we still sure what happened to you that night was deliberate? Nothing else has been done to you.'

'I stay near you – I have perfect protection!' He said it deadpan, though I was trying to decide if there was a trace of irony. 'I felt the hard push,' he reminded me. 'Whoever did that must have known we had collided. He made no call for help when I fell.'

Helena weighed in thoughtfully. 'Marcus, they all know that you are trying to find the killer. Perhaps he is being more careful. He has not attacked you.' Nor had he attacked Helena herself, which at one time had been my unspoken fear.

'I wish he'd try,' I murmured. 'Then I'd have the creep!'

In my head I carried on thinking. This had a bad taste. Either we had missed something crucial, or it would be difficult ever to expose this villain. The vital proof was eluding us. The more time passed, the less chance we stood of solving the mystery.