An aquarium. That was the only way Pitt could describe it. But for the fact that there were no portholes in the walls, the cavern could have easily passed for the main tank at Marineland in California. It was a far cry from the tunnel; marine life abounded everywhere. The lobsters were here, and so were the crabs, the limpets, the barnacles, even a heavy growth of kelp. There were also roving schools of brilliantly colored fish. One fish in particular caught Pitt's eye, but before he could get closer, it saw his approach and flashed into a protective rock fissure.

For several moments, Pitt took in the breathtaking scene. Then suddenly, he started as a foreign hand grabbed his leg. It was Ken Knight, and he was motioning toward the surface. Pitt nodded and swam to the top. Again he was greeted by the heavy mist.

Pitt spit out his mouthpiece. "What do you make of it?" he asked. The rock walls amplified his voice to a roar.

"A fairly common occurrence," Knight answered, roaring back matter-of-factly. "Every time a swell hits the entrance outside, the force runs like a piston through the tunnel, compressing the air already trapped in the cavern. When the pressure recedes, the expanded, moisturized air cools and condenses in a fine mist." Knight paused to blow some mucus from his nose. "The swells are running at about twelve-second intervals, so it should start to clear up at any time."

No sooner had he said it than the mist disappeared, revealing a dim cavern that arched to a dome sixty feet overhead. It was a drowned grotto and nothing more; no traces of man-made equipment. Pitt felt as though he had entered a deserted cathedral whose spires stood in ruined desolation from a World War I artillery shelling or a World War II aerial bombardment. The walls were twisted and broken in jagged fissures, and the shattered rocks at their base showed that another rockfall could come at any time. Then the mist returned and smothered all vision.

Pitt, in the few seconds it took to survey the cavern, was conscious of nothing but the gnawing fear of self-doubt. Then came a creeping wave of numbed disbelief, then the chagrin that he had bungled it.

"It can't be," he muttered. "It just can't be." Pitt's free hand curled into a white-knuckled fist, and he pounded the water in an outburst of temper and despair. "This cavern had to be von Till's base of operations. God help us from the mess that I've surely caused."

"I'd still vote for you, Major." Knight reached out and touched Pitt on the shoulder. "The geology bears out your hunch. This would seem the most logical spot."

"It's a dead end. Except for the tunnel, there's no openings, anywhere."

"I saw a ledge on the far end of the cave. Maybe if I—"