The cracking and groaning sounds continued, and then They could see it on the monitors and hear it coming through the walls.

The giant acrylic sphere burst apart along several of the seams that held its component pieces together. “Tabernacle,” Louise swore, realizing the heavy water must now be mixing with the regular H 2 O inside the barrel-shaped chamber. Her heart was jackhammering. For half a second, she didn’t know whether to be more concerned about the destruction of the detector or about the man who was obviously drowning inside it.

“Come on!” said Paul, heading for the door leading to the deck above the observatory chamber. The cameras were slaved to VCRs; nothing would be missed.

“Un moment,” said Louise. She dashed across the control room, grabbed a telephone handset, and pounded out an extension from the list taped to the wall.

The phone rang twice. “Dr. Montego?” said Louise, when the Jamaican-accented voice of the mine-site physician came on. “Louise Benoit here, at SNO. We need you right away down at the neutrino observatory. There’s a man drowning in the detector chamber.”

“A man drowning?” said Montego. “But how could he possibly get in there?”

“We don’t know. Hurry!”

“I’m on my way,” said the doctor. Louise replaced the handset and ran toward the same blue door Paul had gone through earlier, which had since swung shut. She knew the signs on it by heart:

Keep Door Closed

Danger: High Voltage Cables

No Unauthorized Electronic Equipment Beyond This Point

Air Quality Checked-Cleared for Entry

Louise grabbed the handle, pulling the door open, and hurried onto the wide expanse of the metal deck.

There was a trapdoor off to one side leading down to the actual detector chamber; the final construction worker had exited through it, and had sealed it shut behind him. To Louise’s astonishment, the trapdoor was still sealed by forty separate bolts-of course, it was supposed to be sealed, but there was no way a man could have gotten inside except through that trapdoor…