We were heading into a highly fertile region; a potential grain basket for the Empire. Given that Rome was keen to gain control of the incense trade, I reckoned it would make good sense to shift the trade routes eastwards to this northern capital, ignoring the Petrans' insistence that all caravans turn aside and stop there. Running the country from Bostra instead would provide a more pleasant centre of government, one with a kinder climate and closer links with civilisation. The people of Bostra would be amenable to such a change since it would enhance their current back-row status. And the uppity Petrans would be put in their place.

This wonderful theory of mine had nothing to do with the fact that the Petrans had bounced me out of town. I happen to believe that when you take over any new business, your first task should be to change the personnel so you can run things your own way, and with loyal staff.

The theory might never be implemented in my lifetime, but devising it gave me something to think about when I wanted to stop reading comedies.

Leaving behind us the harsh mountain barrier that enclosed Petra, we had first climbed through the sparse local settlements, then reached more level ground. The desert rolled easily to the horizon on all sides. Everyone told us it was not real desert, compared to the wilderness of Arabia Felix -ironically named – or the terrible wastes beyond the River Euphrates, but it seemed barren and lonely enough for me. We felt we were crossing an old, old land. A land over which varied peoples had rolled like tides for centuries, and would continue to do so in war or peaceful settlement as long as time lasted. A land in which our present journeying was insignificant. It was impossible to tell whether the little crooked cairns of stones beside the road that marked the graves of nomads had been set up last week or several thousand years ago.

Gradually the rocky features diminished; boulders gave way to stones; the stones, which had spread the landscape like acres of roughly chopped nuts on a cooking board, turned into scatters, then were lost altogether in rich, dark, arable soil supporting wheat fields, vineyards and orchards. The Nabataeans conserved their meagre rainfall with a system of shallow terracing on each side of the wadis: wide shelves of ground were held back by low walls some forty or fifty feet apart, over which any surplus water ran off to the terrace below. It seemed successful. They grew wheat as well as barley. They had olives and grapes for oil and wine. Their eating fruit consisted of a lush mixture of figs, dates and pomegranates, whilst their most popular nuts – amongst a handsome variety – were almonds.

The whole atmosphere was different now. Instead of long nomad tents, hump-backed as caterpillars, we saw increasingly pretty houses, each set within its garden and smallholding. Instead of free-ranging ibex and rock-rabbits, there were tethered donkeys and goats.

Once we hit Bostra we were supposed to be meeting up with the remainder of Chremes' company. The group Helena and I had met in Petra were the chief members of the troupe, mainly actors. Various hangers-on, with most of their stage equipment, had been left behind in the north, which did seem friendly, in case the rest found a hostile welcome in the mountains. As far as the murder was concerned, I could virtually ignore them. It was on the first group that I needed to concentrate.

Quite early in the trip I had asked Chremes, 'Why did Heliodorus really go for that walk?' The scenario was still bothering me.

'It was like him to wander off. They all do it – minds of their own.'

'Was it because he wanted a drink, quietly, on his own?'

'Doubt it.' Chremes shrugged. He showed a distinct lack of interest in this death.

'Someone went with him anyway. Who was it?' A long shot, since I was asking the name of the killer.

'Nobody knows.'

'Everyone accounted for?' Needless to say, he nodded. I would check that later for myself. 'Someone else must have fancied a tipple though?' I pressed.

'They'd be out of luck then. Heliodorus never reckoned to share his jar.'

'Might the companion have had his own jar – or goatskin -that Heliodorus had his eye on?'

'Oh yes! That makes sense.'

Maybe the playwright had had an acquaintance nobody else knew about. 'Would Heliodorus have made friends with anybody in Petra, anybody outside your group?'

'I doubt that.' Chremes seemed fairly definite. 'The locals were reserved, and we don't mix much with merchants – or anyone else. We're a close-knit family; we find enough squabbles among ourselves without looking outside for more trouble. Besides, we hadn't been in the city long enough to make contacts.'

'I heard him going up the mountain. I felt he knew the person, he was with.' Chremes obviously realised where my questions were heading. 'That's right: what you say means he was killed by somebody from your group.'

That was when Chremes asked me directly to keep my eyes and ears open. He did not exactly commission me; that, with a fee at the end of it, would have been too much to hope for. But despite his initial reluctance to involve himself, if he was harbouring a killer he wanted to know who it was. People like to feel free to insult their companions or let them pay all of the wine bill without having to worry that it could annoy the kind of man who shoves his travelling companions face down in cold water until they stop breathing.

'Tell me about Heliodorus, Chremes. Did anyone in particular dislike him?' It had seemed a simple question.

'Hah! Everyone did!' scoffed Chremes.

That was a good start. The force with which he said it convinced me that every one of the group from Petra must be a suspect for killing the playwright. On the journey to Bostra, therefore, Helena and I had to think about all of them.

Bostra was a black basalt city built in this blackly ploughed land. It flourished. It had commerce, but it generated much of its own prosperity. There was a fine town gate in distinctly Nabataean architecture, and the King owned a second palace here. To Romans it was alien in flavour – yet it was the kind of city we understood. Irascible donkey-drovers cursed us as we tried to decide where we were going. Shopkeepers looked out from ordinary lock-ups with calculating eyes, shouting at us to come in and see their merchandise. When we arrived, near evening, we were greeted by the familiar scent of woodsmoke from baths and ovens. The tempting odours from hot-food stalls were spicier, but the reek of the leather tannery was as disgusting as any at home, and the stuttering lamp oil in the slums smelled just as rancid as it does all over the Aventine.

At first we were unable to find the rest of the company. They were not at the caravanserai where they had been left. Chremes seemed reluctant to make enquiries openly, from which Helena and I gathered it was likely there had been trouble in his absence. Various members of our group set off to look for their colleagues in the city while we guarded the waggons and luggage. We set up our tent with Musa's silent help. We ate supper, then sat down to wait for the return of the others. It was our first chance to talk over our findings so far.

During the journey we had managed to survey individual members of the group by judiciously offering lifts on our waggon. Then, when Helena grew weary of my efforts at controlling our temperamental ox, she hopped off and invited herself into other transport. We had now made contact with most of them, though whether we had also made friends was less certain.

We. were considering everyone for possible motives -females too.

'A man did it,' I had explained cautiously to Helena. 'We heard him on the mountain. But you don't have to be cynical to know that a woman may have provided his reason.'