'What shall I do with you, then, Gordianus of Rome? To find knowledge is your work, but I will not do your work for you. If I give you the answer you seek, I will rob you of the very means by which you may achieve your end. If you go to Crassus with nothing but a name, he will merely laugh at you or punish you for false accusations. Unless you acquire it on your own, using your skills, the knowledge you seek will be meaningless. That which you assert you must be able to prove. It is the will of the god that I assist you, but I will not do your work for you.'

I shook my head. Of what use was the Sibyl if she refused to utter a simple name? Could it be that she did not know? I cringed at playing host to such impious thoughts, but at the same time it seemed that a veil was being slowly lifted from my eyes and the Sibyl once more began to look suspiciously like Iaia.

Eco touched my sleeve, demanding my attention. With one hand he held up two fingers, and with the other hand turned two fingers down, his sign for a man: two men. He wrapped one hand around the wrist of the other, symbolizing a shackle, his sign for a slave: two slaves.

I turned back to the Sibyl. The two missing slaves, Zeno and Alexandros – are they living or dead? Where can I find them?'

The Sibyl nodded in stern approval. 'You ask wisely. I will tell you that one of them is hidden, and the other is in plain sight.'

'Yes?'

'I will tell you that after they fled from Baiae, this was their first destination.'

'Here? They came to your cave?'

'They came to seek the guidance of the Sibyl. They came to me as innocent men, not guilty ones.' 'Where can I find them now?'

'The one who is hidden you may find in time. As for the one in plain sight, you will find him on your way back to Baiae.' 'In the woods?' 'Not in the woods.' 'Then where?'

'There is a stone shelf that overlooks Lake Avemus…' 'Olympias showed us the place.'

'On the left side of the precipice there is a narrow path that leads down to the lake. Cover your mouth and nose with your sleeve and descend to the very mouth of the pit. He will await you there.'

'What, the shade of a dead man escaping from Tartarus?'

'You will know him when you see him. He will greet you with open eyes.'

It would be a clever place to hide, granted, but what sort of man could pitch his camp on the very shores of Avernus, amid the sulphur and steam and the reeking phantoms of the dead? The stone shelf was as near as I had cared to venture to the place; to descend to its edge sent a shiver through me. I could tell from the way he clutched my arm that Eco disliked the idea as much as I did.

'The boy,' said the Sibyl crisply, 'why does he not speak for himself?'

'He is unable to speak.'

'You lie!'

'No, he cannot speak.' 'Was he born dumb?'

'No. When he was very small he was stricken by a fever. The same fever killed his father; from that day Eco never spoke again. So his mother told me before she abandoned him.'

'He could speak now if he tried.'

How could she say such a thing? I began to object, but she interrupted.

'Let him try. Say your name, boy!'

Eco looked at her fearfully, and then with an odd glimmer of hope in his eyes. It was another strange moment in a day of strange moments, and I almost believed that the impossible would come to pass there in the Sibyl's cave. Eco must have believed as well. He opened his mouth. His throat quivered and his cheeks grew taut.

'Say your name!' the Sibyl demanded.

Eco strained. His face darkened. His Lips trembled.

'Say it!'

Eco tried. But the sound that came from his throat was not human speech. It was a stifled, distorted noise, ugly and grating. I closed my eyes in shame for him, then felt him against my breast, shivering and weeping. I held him tighdy, and wondered why the Sibyl should demand such a cruel price – an innocent boy's humiliation – in return for so little. I drew a deep breath and filled my lungs with the scent of decaying flowers. I summoned my courage and opened my eyes, determined to reprimand her, vessel of the god or not, but the Sibyl was nowhere to be seen.

We left the Sibyl's cave. The cavern of echoes and voices no longer seemed quite so mysterious – a curious enclosure, to be sure, but not the awe-inspiring place it had been when we entered. The way back to the temple was strenuous and rocky, but it hardly required that we crawl; nor was it as long on the way back as it had been on the way to the Sibyl's cave. The whole world seemed to have awakened from a strange dream. Even the fitful fog had receded, and the hillside was bright with afternoon sunshine.

The fire had died in the brazier. The blackened entrails still sputtered and popped occasionally on the hot stone, startling the swarm of flies that circled overhead. The sight was unpleasant, but the smell of charred flesh reminded me again that we had not eaten in hours. In a small recess behind the temple, the boy Damon had strung up and skinned the carcass of the lamb and was carving it with surprising expertise.

We scrambled down the ravine and untethered our horses. Bright sunshine reflected off the maze of rocks, making it as baffling a place as before, if not quite so menacing. We made our way towards the coast. At the crest of a small rise, a glittering expanse opened before us, not the circumscribed sweep of the Cup, but the true sea, an unobstructed body of water extending all the way to Sardinia and beyond to the Pillars of Hercules in the west. The ancient village of Cumae was at our feet.

We rode in silence. On our journeys I usually kept up a running conversation, even if Eco could not answer with his own voice. Now I could think of nothing to say. The silence between us was heavy with an unspoken melancholy.

A wagon driver pointed us to the house of Iaia, which stood perched on a cliff at the far end of the village, overlooking the sea. It was not impressive as villas go, but it was probably the largest house in the village, with modest wings extending to the north and south and what appeared to be another storey stepping down towards the sea on the west. The wash of colours that decorated the facade was subtly original, a blending of saffron and ochre together with highlights of blue and green. The house at once stood out boldly against the backdrop of the sea, and yet seemed an essential part of the view. The hand and eye of Iaia turned everything to art.

The door slave informed us that Olympias had gone out but would return, and had left word that our needs should be attended to. He led us to a small terrace with a view of the sea, and brought food and drink. Presented with a bowl of steaming porridge, Eco began to seem more himself. He ate with relish, and I was heartened to see him shake off his sadness. After eating we rested, reclining on couches on the terrace and gazing at the sea, but I soon grew restless and began to question the slaves about Olympias's whereabouts. If they knew where she was, they would not tell. I left Eco dozing on his couch and wandered through the house.

Iaia had collected many beautiful things in the course of her career – finely crafted tables and chairs, small sculptures so delicately moulded and painted they seemed almost to breathe, precious objects made of glass, ivory figurines, and the paintings of other artists as well as her own. These things were displayed about the house with a great sense of harmony and an unfailing eye for beauty. No wonder she had been so disparaging of Lucius Licinius's taste in paintings and statues.

It was my nose that led me to the room where Iaia and Olympias created their pigments. I followed a strange medley of odours down a hallway until I came to a chamber cluttered with pots, braziers, mortars and pestles. Stacked all about the room were dozens of clay jars, some large, some small, all labelled in the same hand that had signed the portrait of Gelina. I opened the lids and examined the various dried plants and powdered minerals. Some of them I recognized – brown-red sinopis made from rusted Sinopean iron; Spanish cinnabar the colour of blood; dark purple sand from Puteoli; blue indigo made from a powder scraped off Egyptian reeds.