"Naturally!" said Terry. "But first we're going swimming. We haven't had a chance to be overboard since the last time we were here." "We'll be back in time for lunch," Deirdre assured the operator, "but swimming here is so wonderful! We've been talking about it for days!" She went below to change. The operator shrugged. After a further attempt to interest Terry in the celebration of an astronomical first, he went ashore. Terry went with him to get the outboard motorboat he and Deirdre had used before. He was already wearing swimming trunks. A little later the small boat putt-putted away from the _Esperance_ upon the glassy-rippled waters of the lagoon. There was a very great tranquillity everywhere. The booming roar of the surf came from unseen rollers on the reef outside. Seabirds squawked. Palms along the edge of the lagoon waved their fronds very, very gently. "How far will you go before we swim?" asked Deirdre. "All the lagoon's perfect. One place is as good as another." He cut off the motor. "Hmmm. There's a deep place yonder," he observed. "That's where I went with the aqualung and speared the freak fish. Stay away from it." She jumped over in a clean dive. He joined her in the water. She came up, blowing bubbles. "All right, Terry. What are your troubles?" "That bolide bothers me," he told her. "It had a specific destination! It was meant to hit the water over the Luzon Deep!" She dived again. This time Terry followed her. The underwater world was beautifully bright, with ripplings making everything seem to shimmer because of the changing light. When they came up again Deirdre said, "Funny!" "It had a purpose!" insisted Terry. "There were others before it, and they had a purpose too! That's not funny!" "I didn't mean that," said Deirdre. "I meant ... just now, under the water.... What's that?" There was a swirling at the surface, some tens of yards away. It was not the curling eddy made by a fish about to break surface. It was too big a disturbance for that. It looked as if something stirred, barely submerged, but something very large. Terry, staring, thought of a porpoise cavorting just below the ripples. Or perhaps a shark. But sharks and porpoises are too small to have made this eddying. It reappeared. "Get in the boat!" snapped Terry. "Quick!" While she climbed in he let himself sink, his eyes open. There was a clouding of the water underneath, where the surface-disturbance had been. It was mud from the bottom which had been stirred up. He could see nothing clearly through it, though nearby and around him he could easily see the colorings of coral and fan sponges, and he could see small fish darting here and there. He broke surface. Deirdre bent anxiously over the gunwale. "What is it?" "I don't know," he said curtly. "But give me a fish spear." "You won't...." "I just want to have something in my hand," he told her impatiently, "while I look."