The water was cold, but James was too excited to really notice. He slid underwater and started to swim with the current. He could see just enough by the light of the moon to stop himself from bumping into the sides and he moved quickly along, paddling hard with the fins.

Anyone looking this way would see nothing; all that was visible was the narrow top of his schnorkel moving smoothly along the top of the water.

He didn’t dare risk putting his face up to see how far he’d come, but it was taking much longer than he had expected. He seemed to have been swimming for ages. He was just considering taking a quick look above water when he heard a rushing, roaring sound and a deep rumbling that grew steadily louder. And now he saw the water boiling up ahead and a mass of seething white bubbles. The current suddenly got very strong and he found himself being pulled ahead too fast, out of control. He tried to brace himself against the sides, but before he could get a grip he was smashed into a metal grille. He was stuck there, held in place by the force of the water, and his schnorkel was swamped. He fought back the panic, took hold of the grille, and hauled himself sideways across it until he reached the edge.

He had to put his head up to a take a breath and found to his relief that he was underneath a ledge of some sort. He heaved himself out of the churning water and rested on the uneven concrete surface.

He slipped off his sodden knapsack, took out his shoes and two coils of rope and replaced them with the fins, goggles and schnorkel. Then he hid the knapsack in a dark corner, put on the shoes and looped the rope over his shoulder.

Cautiously he crept out from below the shelter of the ledge and looked around. Above him was the funicular railway car, waiting by the piazza. There was no sign of any guards. Presumably they were in their hut, playing cards.

He crawled over until he was behind the car and made doubly sure that there was no one around.

So far, so good.

He looked down the railway. The moon was bright and it was a long way to the tunnel and the big outcrop of rock; luckily, though, the palazzo walls were throwing a wide shadow across the tracks.

He would have to risk it.

He dashed across the tracks into the shadows and started down.

He remembered from the other night how slow and awkward it was negotiating the steep slope and he began to worry that he would be too late. He looked up at the sky. There was still no sign of dawn, but he knew that it wouldn’t be long in coming.