I thought I could find the way in the dark, but it wasn't as easy as I thought.'

'So I myself discovered,' I said.

'We were going too fast, and the wind kept getting stronger, so that we couldn't hear each other shouting, and the fog closed in. Zeno was in a mad panic. Then we took a wrong turn and came to the cliff that overhangs Lake Avernus. My mount knew me, she warned me in time, and even so I almost went tumbling over. But Zeno knew very little about horses. When the beast tried to stop he must have kicked her, and she threw him. I saw him disappear, flying head over heels into the fog. The mist swallowed him up. Then silence. Then I heard a faint, distant splash, like a man falling into shallow water and mud.

'He screamed then. His voice rose up from the darkness – a long, terrifying scream. Then silence again.

'I tried to find a way down to the shore in the darkness, but the trees and fog and shadows baffled me. I called his name, but he never answered, not even a moan. Have I said something wrong?'

'What?'

'The look on your face, Gordianus – so strange, as if you had been there yourself.'

'I was only remembering last night…' I thought of Eco and felt a pang of dread. 'Go on. What happened next?'

'Finally I found the way to Cumae. I entered the house without waking the slaves, found Olympias and told her what had happened. It was Iaia's idea to hide me in the cave. Cumae is a tiny village, they could never have hidden me in the house. Even so, you discovered us.'

'Dionysius discovered you first. You should thank the gods that he didn't tell Crassus. Or perhaps you can thank someone else.' I looked sidelong at Iaia.

'Again you insinuate!' Iaia gripped the arms of her chair.

'Credit me with having eyes and a nose, Iaia. This house is full of strange roots and herbs, and I happen to know that aconitum is among them. On the day we consulted the Sibyl I saw it in a jar in the room where you make your paints. I imagine you might also have strychnos, hyoscyamus, limeum-'

'Some of these I keep, yes, but not for murder! The same substances that kill can also cure, if used with proper knowledge. Do you insist on an oath, Gordianus? Very well! I swear to you, by the holiness of the Sibyl's shrine, by the god who speaks through the Sibyl's lips, that no one in this house committed the murder of Dionysius!'

In the vehemence of her oath, she rose halfway to her feet. As she slowly settled into her chair again, the terrace became preternaturally quiet. Even the crashing of the waves below was hushed. The sun had at last risen above the roof of the house, tracing the terrace wall with a fringe of yellow light. A lonely cloud crossed the sun and threw all into shadow again; then the cloud passed, and the heat reflected from the dazzling white stones was warm against my face. I noticed in passing that the pain in my head had vanished, and in its place I felt a pleasant lightness.

'Very well,' I said quiedy, 'that much is setded, then. You didn't kill Dionysius. Who did, I wonder?'

'Who do you think?' said Iaia. 'The same man who killed Lucius Licinius. Crassus!'

'But for what reason?'

'I can't say, but now I think it is time for you to tell me what you know, Gordianus. For example, yesterday you sent the slave Apollonius diving off the pier below Gelina's house. I understand you made some startling discoveries.'

'Who told you? Meto?'

'Perhaps.'

'No secrets, Iaia!'

'Very well, then, yes. Meto told me. I wonder if we came to the same conclusion, Gordianus.'

'That Lucius was trading arms to the rebel slaves in return for plundered silver and jewels?'

'Exactly. I think Dionysius may have also suspected some such scandal; that was why he hesitated to reveal Alexandros's hiding place, because he knew that there was a greater secret to uncover. Meto also told me that you discovered certain documents in Dionysius's room – incriminating documents regarding Lucius's criminal schemes.'

'Perhaps. Crassus himself couldn't fully decipher them.'

'Oh, couldn't he?'

A faint tracing of pain flickered through my skull. 'Iaia, do you seriously suggest

She shrugged. 'Why not speak the unspeakable? Yes, Crassus himself must have been involved in the enterprise!'

'Crassus, smuggling arms to Spartacus? Impossible!'

'No, quite disgustingly possible, for a man as vain and greedy as Marcus Crassus. So greedy that he couldn't resist the opportunity to reap a huge profit by dealing with Spartacus – surreptitiously, of course, using poor, frightened Lucius as his go-between. And so vain that he thought it would ultimately make no difference to his cause when he gains the command against the slaves. He thinks himself such a brilliant strategist that it won't matter that he has armed his own enemy with Roman steel.'

'Then you say he poisoned Dionysius because the philosopher was close to exposing him?'

'Perhaps. More likely Dionysius had begun to insinuate blackmail, subtle blackmail, merely asking for a handsome stipend and a place in Crassus's retinue. But men like Crassus will not put up with subordinates who hold a secret over them; Dionysius was too stupid to see that there was no profit in the knowledge he was seeking to exploit. He should have kept his secrets to himself; then he might have lived.'

'But why did Crassus kill Lucius?'

Iaia looked down at her feet, where the sunlight had crept close enough to warm her toes. 'Who knows? Crassus came that night in secret to discuss their secret affairs. Perhaps Lucius had begun to balk at the tasks to which Crassus set him and threatened to expose them both; it would be like Lucius to panic. Perhaps Crassus had discovered that Lucius was cheating him. For whatever reason, Crassus struck him with the statue and killed him, then saw a way to turn even that moment of madness to his advantage, by making it look as if a follower of Spartacus had committed the crime.'

I stared out at the unending progression of waves that proceeded from the horizon. I shook my head. 'Such supreme hypocrisy – it's almost too monstrous to be believed. But why, then, did Crassus send for me?'

'Because Gelina and Mummius insisted. He could hardly refuse to allow an honest investigation of his cousin's death.'

'And how did Dionysius come to have the documents?'

'That we can't be sure of. The only thing we know for certain is that we shall never have an explanation from Dionysius's lips.'

I thought of Crassus's dark moods, his unspoken doubts, his long nights of searching through the documents in Lucius's library. If all was as Iaia had concluded, then Crassus was killer, eulogist, judge, and avenger combined, beyond the power of any of us to punish.

'I see you are not entirely satisfied,' Iaia said.

'Satisfied? I am most dissatisfied. What a waste, what futility, to have put myself in such danger, and not only myself – Eco! All for a bag of silver. Crassus solves all his problems with silver – and why not, when men like me will settle for mere coins. He might as well have sent me the money and allowed me to stay in Rome, instead of dragging me here to take part in his hideous deception-'

'I meant,' said Iaia, 'that you might not be satisfied with my explanation of events. There are certain other circumstances of which you know nothing, which might grant you a little more insight into the workings of Crassus's mind. These matters are so delicate, so personal that I hesitate even now to discuss them with you. But I think Gelina would understand. You know that she and Lucius were childless.'

'Yes.'

'And yet Gelina very much wanted a child. She thought the problem might lie with her, and she sought my help; I did what I could with my knowledge of medicines, but to no avail. I began to think the problem rested with Lucius. I brewed remedies which Gelina administered to him in secret, but that was of no use, either. Instead, Priapus eventually withdrew his favour from Lucius entirely. He became crippled in his sex – powerless, just as he was powerless to control his own life and destiny. Imagine being Crassus's creature, compelled to fawn over his greatness, reduced to tawdry schemes of escaping his domination – which Crassus would never allow, because it gave him a perverse pleasure to keep his cousin pressed beneath his foot.