Paul’s voice-now coming from back in the control room-was barely audible above the air-conditioning equipment and the sloshing of the water in the huge cavern beneath Louise’s feet. “If that man’s still alive,” he shouted, “he’ll see the lights up on the deck through the trapdoor.”

Louise nodded. The only thing the man would now be seeing was a single illuminated square, a meter on a side, in what, to him, would be a vast, dark ceiling.

A moment later, Paul returned to the deck. Louise looked at him, then back down at the open trapdoor. There was still no sign of the man. “One of us should go in,” said Louise.

Paul’s almond-shaped eyes went wide. “But… the heavy water-”

“There’s nothing else to do,” said Louise. “How good a swimmer are you?”

Paul looked embarrassed; the last thing he ever wanted to do, Louise knew, was look bad in her eyes, but… “Not very,” he said, dropping his gaze.

It was already awkward enough down here with Paul mooning over her all the time, but Louise couldn’t very well swim in her SNO-issue blue-nylon jumpsuit. Underneath, though, like almost everyone else who worked at SNO, she only had on her underwear; the temperature was a tropical 40.6 Celsius this far beneath Earth’s surface. She yanked off her shoes, then pulled on the zipper that ran down the front of the jumpsuit; thank God she’d worn a bra today-although she wished now that it hadn’t been as lacy.

“Turn the lights back on down there,” said Louise. To his credit, Paul didn’t tarry. Before he’d returned, Louise had slipped through the trapdoor into the cold water; the water was chilled to ten degrees Celsius to discourage biological growth and to reduce the spontaneous noise rate of the photomultiplier tubes.

She felt a rush of panic, a sudden feeling of being a long way up with nothing supporting her; the bottom was far, far below. She was treading water, her head and shoulders sticking up through the open trapdoor into the air, waiting for her panic to subside. When it did, she took three deep breaths, closed her mouth tight, and dived beneath the surface.