The conditions were absolutely amazing. The vis, he noted, had to be at least seventy feet, the water almost totally free of particulate matter so that the kelp and rocks seemed trapped in glass. All around them fish swam in large numbers. He counted half a dozen types of rockfish alone, their distinctive striped bodies hovering in the water like a fleet of zeppelins.

The bottom fell steeply, and it wasn’t long before they came to the sandy slope that marked the beginning of the edge of the canyon. The sand here was dotted with Pachycerianthus fimbriatus, the tube-dwelling anemone, as well as colonies of Phragmatopoma californica, the purple-armed tube worms that reminded him of the wild asters that had grown along the side of his grandparents’ house. Where the anemones were scattered singly over the bottom, the tube worms bloomed in tight groups like living bouquets.

Farther down the slope the water became dark, almost ominous in color. There the visibility lessened, and where the colder water of the deep canyon met the warmer water of the upper surface, a thermocline formed a rippling ribbon that stretched across the edge of the canyon like a warning. Beyond it the bottom dropped off into the abyss of the canyon. Ben checked his computer and saw that they were at a hundred and nine feet.

Caddie was looking at one of the tube worms, her head down while her feet kicked gently behind her. Brian, ahead of her, was following what looked like a halibut, waiting for it to settle into the sand and then poking it to watch it rise, flying-carpet-like, and swim away from him.

Ben looked out into the shadows that seemed to stretch as wide as the universe. He wondered if either Caddie or Brian realized what an unusual thing they were seeing. Ben had seen the view many times but still it awed him, even frightened him. Hovering on the edge of the canyon, one had the sense that it was very much possible to suddenly fall in, to be swept down thousands of feet by a treacherous current that roamed the perimeter, dragonlike, waiting for the curious and the foolhardy.

Although Ben knew that no such current existed, the sense of dread so many divers experienced when diving in this place made him cautious. It was possible to lose track of depth and descend rapidly to dangerous depths without even realizing it. And there was the lure of the canyon itself. More than one diver had swum into it and disappeared, and although these deaths were almost certainly deliberate choices, he wondered sometimes if those unfortunate souls hadn’t been following some voice only they could hear.