It was coming from two lamps which were set on either side of a jetty, and at the end of the jetty was a boat, bobbing up and down gently.

Elissa embraced Tisamenos, then, looking at Silvius over his shoulder, she beckoned him, and gratefully he joined her.

The creature hissed at them, ‘No delay.’ Its voice was so cold and powerful they had to obey.

It creaked past them and flowed into the boat, taking up position at the helm. The boat was an unpainted thing that looked as if it might be full of holes. Silvius was suddenly terrified in that blank space where nothing grew or lived, with only the dull sound of black water washing against the muddy banks and the featureless face of their companion, white in the lamplight.

‘You are the ferryman,’ said Silvius quietly. ‘I will not get on your boat. You take souls into the Underworld.’

‘Safe passage,’ hissed the ferryman. ‘I take no gift.’

‘How do we know?’ Silvius said. ‘You brought us here against our will.’

‘Look here.’

From out of the shadows, a figure emerged. The lower half a beast, the upper part human. For a moment Silvius thought it was Stargazer’s spirit, come to help them in the Underworld. It came further into the light. A mane, glowing with health and colour. A woman, clothed in white, pearl-eyes staring.

Riding on her lion, it was the Sibyl.

Silvius felt a great rush of relief.

She greeted them; Elissa had already buried her face in the lion’s mane in welcome. ‘I came from Sicilia through the dark ways to aid you, as my mother did your father Aeneas when he came to the Underworld. Python gathers an army. He will consume everything in his path, including those that remain here.’

‘We are few …’ said the ferryman. ‘King and queen long gone, through a gap in time. I saw them go. World of ice. I stayed. I ferry the souls. They come still, sometimes.’ It was the longest Silvius had heard him speak, and there was a desperate, dull sadness in the words.

‘Where else do they go?’ asked Tisamenos.

The ferryman shrugged. ‘I know the river, the two banks. The stones and the earth.’

Dismounting, the Sibyl deftly embarked. With a leap, the lion followed her, and Silvius was relieved to see that the boat remained steady.

‘We go this way,’ said the Sibyl, ‘and bring you out by the ruins of Troy. You cannot return, as the ghosts will only let you pass once – until it is your time.’

‘I do not wish to come back here,’ said Silvius.

‘I want to see the sea again,’ replied Elissa.