It had stopped. It was present yesterday, and even during the night, when La Rubia came into the lagoon. But now the sea held no sound other than the multitudinous random noises of fish and the washing, roaring, booming of the surf.
Deirdre was aboard, of course. She watched Terry's face. He turned to the new instrument, and then dropped his hand.
"I think," he said carefully to Davis, "that I'd like to make a sort of sweep out to sea. It's just possible we'll find the hum farther out."
Deirdre said quickly, "I think I know what you're up to. You want to survey a large area of the ocean while something comes up. Then you can direct that "something" to the lagoon mouth by using your sound device, so the ... whatever-it-is has to take refuge in the lagoon. Since we've killed the squid...."
"That's it," said Terry. "Something like that happened when we speared the fish. The squid took their place. Now we've killed the squid. Just possibly...."
They found the humming sound in the water four miles off-shore. They traced it through part of a circle. If something were being driven upward, it could not pass through that wall of humming sound.
"That proves your point," Davis said. "Now what?"
Without realizing it, he'd yielded direction of the enterprise to Terry, who had unconsciously assumed it.
"Let's go back to the island," said Terry thoughtfully. "I've got a crazy idea—really crazy! I want to be where we can duck into shallow water when we try the new projector."
The Esperance swung about and headed back toward the island. The sea and the distant island looked comfortingly normal and beautiful in the sunshine. Under so blue a sky it did not seem reasonable to worry about anything. Events or schemes at the bottom of the sea seemed certainly the last things to be likely to matter to anyone.