‘And the sun.’ Tisamenos held his hand out to Elissa, and she took it gratefully, clambering onto the boat beside the lion and immediately burying her face in his mane again. The beast flicked his tail in response. Silvius, however, ignored the other boy’s gesture, and jumped on by himself, sitting a little way apart by the Sibyl.

Once they were all on board, the boat seemed to have expanded. The lion’s head was raised, but even he was subdued, his eyes dulled.

The ferryman pushed off, and rowed them out into the dark, swirling waters of the River Styx. The blackness was infinite, the oar strokes were slow, and the water that splashed them was freezing.

Hollow booms sounded in the distance. The monsters of the Underworld that Silvius’s father sometimes spoke of – might it be them? Or might the ancient Titans be tortured still for their crimes? He shuddered, and snuggled into the lion, which kept him warm as the boat made its way steadily onwards into the darkness.

Soon the lights of the jetty behind them had gone, and ahead was only the water and the blackness and the cold and that terrible loneliness.

Silvius did not dare to speak. The space around them might steal the words from his lips, might suck his life out through his mouth, pull him into watery oblivion.

Tisamenos clutched the Last Gorgon’s head in its sack between his knees; Elissa clamped onto the quiver as if it were a branch and she a drowning girl. Silvius stared out into the blackness. He didn’t miss the Arrowhead, but he still hadn’t quite made sense of the vision that it had given him, and now that Elissa had the quiver, he wondered what role was left for him to play. Was he needed, now that Tisamenos had come along? Would Elissa be able to carry the Bow and Arrow by herself? The Sibyl’s sightless eyes seemed to glow in the gloom as she stroked her lion’s mane. All the time the ferryman rowed, his oars slipping in and out of the water.

And at last lights appeared ahead of them, beacons in the murk, and the boat cut on through the sluggish waves, until it bumped against the shore, and the ferryman slipped out.

As Silvius passed him he bowed again, and whispered something that sounded like, ‘Go well.’ But Silvius thought, for a moment, that he might have been saying, ‘Save yourselves.’

He slid back into his boat and cast off, and soon he was gone, the companions alone on the far side of the Styx, in the depths of the Underworld. The ground was harder here, and the light was now a kind of grey shimmer. Even the Sibyl and her lion looked insubstantial.

From ahead, rumbling and loud, came a sound like a great roar.