Louise could see clearly, and her eyes didn’t sting at all. She looked around, trying to spot the man, but there were so many pieces of acrylic, and There he was.

He had indeed floated up, and there was a small gap- maybe fifteen centimeters-between the top of the water and the deck above. Normally it was filled with ultrapure nitrogen. The poor guy must be dead; three breaths of that would be fatal. A sad irony: he probably fought his way to the surface, thinking he could find air, only to be killed by the gas he inhaled there. Breathable air from the open trapdoor must now be mixing with the nitrogen, but presumably it was too late to help him.

Louise pushed her own head and shoulders up through the trapdoor again. She could see Paul, desperately waiting for her to say something-anything. But there was no time for that. She gulped more air, filling her lungs as much as she could, then dived under. There wasn’t enough room for her to keep her nose above water without constantly banging her head into the metal roof as she swam. The man was about ten meters away. Louise kicked her feet, covering the distance as quickly as she could, and A cloud in the water. Something dark.

Mon dieu!

It was blood.

The cloud surrounded the man’s head, obscuring his features. He wasn’t moving at all; if he were still alive, he was surely unconscious.

Louise craned to get her mouth and nose into the air gap. She took one tentative breath-but there was plenty of breathable air there now-then grabbed the man’s arm. Louise rolled the fellow over-he’d been floating facedown-so that his nose was sticking up into the air gap, but it seemed to make no difference. There was no spluttering from him, no sign that he was still breathing.