The job accomplished, Zavala brought the metal arms back to their rest position and increased throttle. With Austin still on the sub's back, they plunged through the hole and into the lagoon. The thirty-foot visibility was cut in half by thousands of tiny particles of seaweed that had washed into the cove to be shredded by the razor-sharp rocks. The sub slowed to a walk, Zavala feeling his way like a blind man with a white cane. They didn't see the huge object until they were almost on top of it. Again the sub came to a stop.

“What is that thing?” Zavala asked.

The cathedral light filtering down from the surface illuminated an enormous structure. It was about three hundred feet wide, Austin estimated, and about thirty feet thick, tapered at the ends like a huge metal lens and resting on four thick metal legs. The legs were hidden by boxlike structures where they sank into the sea.

“It's either a big metal spider or a sunken UFO,” Austin said in wonder. “In any case, let's take a closer look.”

At Austin's direction, Zavala steered the sub off at an angle and cruised along the perimeter as far as they could, then retraced their path and went along the other side. The structure was almost perfectly round except where it butted up close to the undersea cliffs. “Hey, this is amazing! I'm getting high heat readings.”

“I can feel the heat through my wet suit. Someone has cranked up the BTUs.”

“The instruments indicate that it's coming from the pillars. Must be conduits as well as supports. Nothing dangerous. Yet.”

“Park this thing while I go in for a closer look.”

The mini dropped lightly to the bottom and rested on its pontoons. Austin unhooked the harness and peeled off with instructions for Zavala to turn on the positioning strobe light in fifteen minutes.

Austin swam toward the disk, then over it. Except for a circular skylight the odd structure was fabricated of metal painted a dull green, which would have been difficult to see from the surface. He dropped down onto the dome itself and peered cautiously through the skylight.

Below was a network of pipes and machines. Men in white frocks walked about the well-lit cavernous space. Austin puzzled over the function of the machines, trying to put what he saw together with the hot water discharges, but came up with nothing. He undid a portable waterproof video camera from his belt and filmed the scene below. Satisfied with his work, he decided to get an overview. He rose off the disk and was panning the camera when he saw movement out of the corner of his eye.

He froze, floating above the structure. The egg-shaped elevator Zavala had described descended from the shimmering surface. It moved along its track and disappeared into a circular hatch that was opening on the roof of the underwater structure closest to the face of the cliff. Austin resumed his camera work only to be interrupted again, this time by Zavala.