“What is it?”

He rewound the tape, turned up the gain, adjusted the 31-band equalizer to filter out some of the white noise, played it again. “Not sure.”

“One of the target hulls crushing on its way down, maybe?”

He just shook his head, played it again, held the headphones tight against the sides of his head. “Sounds biological. Maybe geological. Maybe. Like a thermal vent at the bottom or something? But my bet is biological.”

The tone of the Admiral’s voice was dismissive. “It’d have to be huge to—”

“You brought me in because you’ve been lighting off atom bombs under water, and now suddenly your sub guys are hearing strange noises. You brought me in, me, because I’m the expert, and I cash the check whether you believe me or not.” He took the earphones off. “Just saying.”

“I apologize.” The Admiral held up his hands. “So what kind of… biological… are we talking?”

“Well, you’re right about one thing. It would have to be huge. Bigger than a blue whale, maybe twice as big. But that’s not what worries me.”

“What worries you?”

“Every time we hear it, it’s at a shallower depth. And it sounds angry.”