The walls surrounding the deck were covered with dark green plastic sheeting to keep rock dust out. Dozens of conduits and polypropylene pipes hung from the ceiling, and steel girders sketched out the shape of the room. Computing equipment lined some walls; others had shelves. Paul was over by one of the latter, desperately rummaging around, presumably for pliers strong enough to crank the bolts free.

Metal screamed in anguish. Louise ran toward the trapdoor-not that there was anything she could do to unseal it with her bare hands. Her heart leapt; a sound like machine-gun fire erupted into the room as the restraining bolts shot into the air. The trapdoor burst open, slapping back on its hinges and hitting the deck with a reverberating clang. Louise had jumped out of the way, but a geyser of cold water leapt up through the opening, soaking her.

The very top of the detector chamber was filled with nitrogen gas, which Louise knew must be venting now. The water spout quickly subsided. She moved toward the opening in the deck and looked down, trying not to breathe. The interior was illuminated by the floodlights Paul had turned on, and the water was absolutely pure; Louise could see all the way to the bottom, thirty meters below.

She could just make out the giant curving sections of the acrylic sphere; the acrylic’s index of refraction was almost identical to that of water, making it hard to see. The sections, separated from each other now, were anchored to the roof by synthetic-fiber cables; otherwise, they would have already sunk to the bottom of the surrounding geodesic shell. The trapdoor’s opening gave only a limited perspective, and Louise couldn’t yet see the drowning man.

“Merde!” The lights inside the chamber had gone off. “Paul!” Louise shouted. “What are you doing?”