I took a step towards him and he tried to lift his head, but fell back with a groan. I saw that the rope which bound his arms was also tethered to the ankle-chain, so that he could not move or ease a single limb without experiencing agony. The shoulders of his tunic were stained with stripes of blood. Someone had whipped him savagely, by the look of it.

‘What do you want? And what are you doing here? You’re not Lavinius.’ His voice was weak with pain, but he was sullen too. ‘Have you come to torment me a bit more?’

I was aware of Modesta, behind me, craning to look in. I gestured her to stand a little further off and moved to squat down on a lumpy sack where he could see my face. Inside, the room was dank and smelt strongly of something old and vegetal: overripe turnips or damp nuts, perhaps.

‘I’ve come to ask about your missing passenger. She was a Vestal Virgin, as of course you know, and a most important person. Far more important than either you or me – you cannot expect her relatives to simply let it pass.’

With a painful effort he turned his head away (almost the only part of his body that he could move at all) and maintained a stubborn silence. It was a foolish gesture, in the circumstance – anyone from the household would have had him flogged for it – but I could not fault his spirit or his bravery.

I tried again, though I was talking to his averted cheek. ‘You were responsible for delivering her safely to her bridegroom, and in that you failed. You can hardly be surprised if they have locked you up.’

In fact I felt some sympathy with the prisoner. This was a miserable place to be chained up but, judging by the hoop to which the ankle-chains were fixed and the expert way that his bonds had been arranged, he was not the first to be incarcerated here. This was clearly where errant household slaves were held while they were awaiting serious punishment. Most large establishments have some provision of the kind – though in general offenders do not have to share their prison with stores of vegetables.

The captive muttered sullenly, ‘I’ve already told them everything I know. I saw the wretched woman get into the seat and put the shutters up – that was the last I saw of her.’

‘And you drove straight to Glevum after that?’

No answer.

A sudden inspiration came to me. This man was almost certainly a Celt – as I was myself – but here was I approaching him in formal Roman dress. I could not tell for certain what his clan might be, because he wore the now-ubiquitous short brown Roman tunic instead of traditional Celtic breeches made of tribal plaid, but he was fairish and I guessed that he came from the local Dubunni. I, of course, had been captured further south and dragged to Glevum by a slave trader, so our respective dialects were no doubt different, but I was fairly sure that he would understand me if I used my native tongue and I hoped he might be more inclined to answer if I did.

But first I had to win his confidence. ‘Modesta,’ I said, rising to my feet. ‘Fetch the chief slave and tell him to come here, and bring a knife to free these bonds a bit. I cannot usefully question a man who is in too much pain to speak.’

The girl looked startled but she scuttled off.

I squatted on the sack beside the man again and said softly, in Celtic, ‘Raedarius, I too have been given an unwelcome task. The bridegroom and my patron – who are hugely rich, important men – have charged me with finding out what happened to the bride. If she didn’t come to Glevum, she must be somewhere else, and if I can find her (which I am very doubtful of) it might be possible to get you out of here.’

A moment’s silence, before he answered in the same tongue. ‘You would do that, citizen?’

‘For a fellow Celt. Especially if we prove you had no part in it. But I can’t do anything if you will not assist. So I ask a second time – did you come straight to Glevum, when she’d got into the coach?’

He made a huge effort and turned his face to me again. When he spoke, his voice was tight with pain. ‘I’d like to say so, citizen, but it is not quite true. I’ve thought about it half a dozen times. She was sitting in the raeda, I assisted her myself, but then I had to go upstairs and get her other box. It was a large one, very heavy – full of gifts she had been given, I believe – and she wanted it to ride inside the coach with her. She already had her jewel box in there for security.’

I nodded. Carrying valuable goods inside was not unusual – most travellers did it if they could as it helped discourage thieves. ‘So you went up for the box?’

‘Exactly, citizen. And that was the last time I can absolutely swear to seeing her, because the box was so heavy that I could not manage it. I had to send for two of the house-slaves to bring it down for me. Her handmaiden watched them put it in the coach while I saw to the horse.’

I interrupted him. ‘Ah, the maidservant, who disappeared as well? So she was with Audelia in Corinium? You can vouch for that?’

‘Of course she had a maid there,’ he said, reluctantly. ‘An important lady like that would not travel far alone. Indeed, for several days – apparently – she had a mounted guard as well.’

‘So what became of him?’

‘He left this morning – going the other way, I understand. She had left some things behind the day before and the rider was sent back to recover them.’

I felt at once this was significant. ‘It must have been something of great importance!’ I exclaimed.

Despite his discomfort he managed a wry smile. ‘She seemed to think so, citizen. She was quite distraught. A pair of special wedding slippers, I believe it was. She did not discover the loss till after we arrived last night, I understand, when she went to show them to Lavinia and found they were not there.’

Wedding slippers! I had not expected that, I had been imagining the loss of jewels or gold. But this was a more endearing picture of Audelia. Although she was marrying so late, she would be a virgin still – Vestals who infringed their vows in that respect faced an appalling death – and like any first-time bride, naturally she’d want the special trappings of the day. The shoes would be especially important to a Vestal, too, since most of her other clothes looked like a bride’s in any case.

I remembered the only time that I had seen a Vestal was when I was in Londinium once. I had actually commented that she looked dressed for marriage, then: the same special hairstyle divided into six, the light-coloured stola and the carefully knotted band around the waist which can only be untied for a husband – or a deity. It was explained to me that these were all adopted when the priestess joined the hearth as a sign of her being spiritually wedded to the shrine. So only the distinctive saffron-colour of the bridal veil and shoes, instead of the white versions which she usually wore, would mark Audelia’s marriage-day. ‘No wonder the poor woman was distressed at leaving them behind,’ I said.

‘It was the maidservant who was to blame for it, of course,’ the driver said, moving his shoulders slightly as if to ease the ache. ‘The Vestal was so proud of them, and so excited that she was at last to be a bride, the girl was sent to get them from the box at every stop they made, to show them off. Only this time, it seems she forgot to put them back.’

I looked at him suspiciously. ‘How do you know all this?’

‘Puella, the maidservant, told me so herself.’

‘You talked to her?’

He made a woeful face. ‘That box took up so much room there was no space for her inside – there was less room in my carriage than the one they’d had before – so she had to come and ride with me on the bench-seat in front.’ I realized that, although speech was agony, he was now keen to help me if he could. ‘Of course, she swore that it was not her fault – she’d put the shoes back as she always did – and someone must have moved them afterwards.’ He caught his breath in pain. ‘But of course she couldn’t have. Took them out to look at them herself, I rather think. They were finest leather and quite exquisite, she said, a parting present from a grateful, barren wife for whom the Vestal had once offered sacrifice – and who had then gone on to bear a son. Audelia was heartbroken to find that they had gone.’

‘Had Puella been guilty of such a lapse before? Indeed, had she been with the Vestal very long?’ I was suddenly suspicious. It occurred to me that attendant servants at a shrine are usually slaves of the temple as a whole, and not owned by any individual. I wondered how much Audelia knew about her careless maid.

‘Acquired for the journey, as I understand. A gift from another grateful supplicant, which only made the situation worse. Puella was a pretty little thing, but you could see that she was terrified. She’d been promised freedom when she got here, I believe, and obviously she feared that she had lost her chance and that a fearful beating was awaiting her instead. I think she was quite glad of the excuse to ride outside with me, despite the fact that it was raining heavily.’

These wedding shoes were interesting me. Was it possible the maid had left them out deliberately? Or had she packed them, as she claimed she had, and someone else had really moved them later on? But either way, what purpose did it serve? And then it struck me: it removed the guard.

‘Who suggested that Audelia should send the rider back?’ I asked.

It was more and more painful for him even to draw breath. ‘Citizen, I fear I cannot answer that. I was in the stable, sleeping near my horses as I always do, to keep an eye on them. By the time I was sent for the decision had been made.’ He winced. ‘Have you nearly finished with your questioning?’

‘Not quite. If we hope to find Audelia you must tell me all you can. You did not think it strange that they sent away the mounted guard?’

He took a sobbing breath. ‘Not really, citizen. I was there to guard her the remainder of the way – after all I had guarded Lavinia until then. And anyway, what else was there to do, if Audelia really wanted to have her slippers for the marriage feast? If the rider set off at first light there was a good chance that he would manage to retrieve the shoes in time, especially if he brought them directly to this house: a man on horseback can travel twice as quickly as a coach. It wasn’t my idea, but if I’d thought of it, I might well have suggested it myself.’

It seemed a cruelty to ask him any more, but I had no choice. ‘So where had Audelia left the shoes?’ I asked. ‘Another lodging-house? I understood that she had only assented to this stop, because the owners were known to her uncle’s family.’

‘There were other stops, of course. It took her several days to make the journey from the shrine, I understand.’

But of course it had, I thought. It’s not as if she were an Imperial messenger, with relays of fresh horses every mile or two. ‘A Vestal pilentum is notoriously slow and dignified,’ I said. ‘I suppose he would have to stop somewhere overnight each time. Doubtless the family had arranged it all.’

‘Glad to stop too, I shouldn’t be surprised, in an old-fashioned coach like that. I saw it in the stable-yard and had a look at it.’ Talk of his trade brought animation to his face. ‘Two horses – like a raeda, but much more cumbersome. A little bit more padded, but extremely slow.’ He was so engrossed that he almost tried to rise, only to sink back with a painful groan. When he spoke again, he sounded more subdued. ‘Puella said they stopped at several households on the way – most of them friends or distant relatives of Lavinius. It was all arranged before they left the temple, anyway. A Vestal Virgin doesn’t stop at common inns. But I can’t tell you anything about all that. I only collected her at Corinium.’

There was a movement at the doorway and Modesta sidled in, looking in astonishment at the pair of us speaking in a language which she clearly didn’t understand.

‘Well?’ I said in Latin. ‘Have you news for us?’

‘Citizen, the steward’s on his way,’ she said in the same tongue. ‘I thought you ought to know. There has been a message that the banquet will take place after all. The master and the bridegroom are already on their way, Publius managed to use his influence and borrowed a carriage to bring them here as soon as the games ended. They will not be very long. When they come, I’ll bring them out to you.’ She darted me a timid little smile. ‘Don’t let the master catch you talking foreign languages, though, or he’ll think you two are plotting and chain you up as well.’

The raedarius made an outraged, strangled sound. ‘But . . . !’

I kicked his leg to warn him that he should hold his tongue. I knew what he had been tempted to retort: that Latin, if anything, was the foreign language here, and that what we were speaking was her ancestral tongue, but it is not wise to voice an argument like that – especially if you are at the mercy of a high-born Roman at the time.

I need not have worried. The captive took my hint and said not another word until the maidservant had sketched a bow and scuttled off.