Twenty minutes later James was standing knee deep in the clean, crystal-clear waters of the Mediterranean. He had already put on the fins and a clip to stop anything from going up his nose, and now he clamped his teeth around the hard rubber of the schnorkel’s mouthpiece and slipped the goggles over his eyes. He felt strangely claustrophobic and panicky. The goggles narrowed his vision and he had to concentrate on his breathing for a while so as not to hyperventilate. When he felt more relaxed he waded out a little further and tentatively dipped his face beneath the surface. The underwater picture snapped into focus and he gasped with surprise. It was like suddenly peering through a window into another world. One moment he had been in a bright world of harsh sunlight and vivid colours, and the next he was in a quiet, gloomy, liquid world of shifting shapes and murky yellows and greens. From above he had been able to make out nothing of this world under the water, the picture had been fractured and blurred; but now he was in it and he could clearly see a shoal of tiny silver fish nosing around his feet.

He laid his body flat and kicked lazily with his fins. They sped him through the water without making a splash and he marvelled at the new sights.

He glided over a bare stretch of sand and into a forest of sea grass. A shoal of striped sea bream, with black bands around their tails, broke in two as he approached and scattered briefly before regrouping. Then he spotted some larger fish, brown meagres, and a great pipefish, long and thin, like a piece of drifting seaweed. He swam deeper until he was past the sea grass. Below him now was an alien landscape of fan mussels, Neptune grass and slimy black sea slugs, which gouged long trails as they dragged themselves through the sand. He headed towards a large rock that stood like a mountain, its top rising above the water. Starfish and urchins clung to its side, and sea anemones, their delicate pink fronds waving in the water. A spiny spider crab, with long gangly legs, poked about looking for scraps.

James peered into a crack and saw two great gloomy eyes peering back at him. He smiled and moved on, and as he swam out past the rock the seabed suddenly fell away. His breath caught in his throat when he found himself suspended in endless deep blue sea, surrounded by teeming shoals of fish: red mullet, bream and beautiful little wrasse with yellow-striped bodies and pale blue heads.

James hung there watching the fish until he decided to go deeper and see if there was anything bigger out there. He swam on, feeling tiny in this great blue void. He soon lost all sense of time and space and it was only when he heard the dull throb of an engine that he was brought back to reality.