"Don't go too deep," the divemaster warned them. "Stick to the reef. And remember to check your gauges. You should have enough air for an hour at that depth, so be back here in forty-five minutes. Got that?"

The diving party mumbled their acknowledgements then lined up to enter the water. In the moonlight the sea was an oily black, with patches of silver that skittered across the waves. It was perfect for a night dive. As each diver left the boat and plunged into the water, they sent out wavelets that set the reflected moonlight dancing before becoming lost in the boundless ocean.

As she waited her turn, Angela checked her diving gear. She fitted her regulator, and the taste of warm rubber filled her mouth, followed by rush of cold, metallic air as she took her first breath from the tanks on her back.

"Ready?" the divemaster asked her. Angela nodded and gave him the 'OK' signal. "In you go then."

And she did.

Angela rolled into the water. Instantly, the shock of the cold sea hit her, leaving her breathless. Angela adjusted her regulator and breathed in deeply. Then, with with a flick of her fins, she turned so she was facing towards the reef a dozen metres below her. Already it was illuminated by the torches of the other divers, their beams cutting through the darkness like great blades of light. Angela swam down to meet them, leaving a rope of bubbles behind her.

At night the reef seemed to glow. Small creatures emerged from holes between the rocks; flickering fronds darted out from the masses of coral. However, the beauty of it faded away in the harsh incandescence of the divers' lamps. Determined not to lose it, Angela turned off her own torch and moved away from the group in search of a deserted patch of reef. Then she hung there, suspended in the water, lost in contemplation.

As her eyes grew more accustomed to the darkness, Angela began to see shapes in the water: clouds of particles, translucent spheres, sinuous ribbons; glowing blue, white and green. These forms shifted and moved, making them impossible to focus on. Angela checked her watch. She had only been down here for twenty minutes. There was plenty of time before she had to come back to the boat. And these things were not far away ... .

Angela turned in the water and, with a volley of strong kicks, headed towards the brightest of these lights. Behind her, the lights of the rest of the diving party faded and dimmed.