Deirdre stared at him, frightened. She swung the boat's bow shoreward. The outboard motor roared, and the boat raced past the gap in the reef and rushed toward the lagoon opening.
"Are you all right? What happened? You were swimming and suddenly...."
He swallowed. His hands quivered. He shook his head and then said unsteadily, "I meant to ... check the reason those queer fish stay in the lagoon. I thought that if they belonged in the depths and were somehow carried out of them, they would try to get back. I found out!"
He felt an unreasonable relief when the lagoon entrance was behind the boat. The glassy water was reassuring. The Esperance looked like safety itself.
"I think I know how they got here, now," he added. "We underestimated what we're trying to understand. I'll be all right in a minute."
It was less than a minute before he shook himself and managed to grin wryly at Deirdre.
"Was there a hum in the water?" asked Deirdre, still staring at him. "I thought I heard it on the bottom of the boat. Was that the trouble?"
"Yes. I wouldn't call it a hum," Terry admitted. "Not any longer. Now I know what a slow fire feels like."
"You frightened me," said Deirdre, "the way you splashed...."
"I heard the humming sound," said Terry, "last night when the yacht came up to the island. We were perhaps a half-mile off-shore. It was very faint, but I had the amplifier turned down low. The hum was at its loudest just before we passed the reef, but nobody else noticed. When Dr. Morton said there were abyssal fish in the lagoon, I knew why they'd be there. I made a guess at what might drive them there. I went to find out if I was right. I found out!"