The swift current bled north into a deepwater inlet, and I knew the basin had to be close. And then my headphones were accosted by clicks, the bizarre underwater acoustics coming from multiple contacts in the river directly ahead.

I slowed to five knots, my heart pounding in my chest.

Ben moaned something in his delirium.

“Shh!”

“Are we topside yet?”

“We’re en route to the extraction point. Be quiet. Something’s between us and the northern basin. Whatever they are, there seems to be a lot of them.”

“I’m dying back here and you’re messing with more fish? Just pound the horn and scare ’em outta the way.”

Before I could stop him, Ben overrode my sonar control, switching from passive to active a second before he repeatedly pinged the depths.

Ping… ping… ping…

I unclipped my harness and leaned over the back of my seat to his console, grabbing his wrist before he hit the device again. “Are you nuts?”

“Take me home!”

Leaving me no option, I punched his wound, the pain rendering him unconscious. Wheeling back around, my eyes focused on the sonar monitor as my hands worked at re-securing my harness.

They had been sleeping upright in the water like sixty-foot logs. Now, as their brains awoke, the pods of Livyatan melvillei mothers and calves began bombarding the river with bursts of echolocation that rattled the sub like a giant tuning fork.

Zzzzzzzzzzt… zzzzzzzzzzzzzt…

I turned to starboard as a two-story, charcoal-gray head charged out of the murk. The creature’s ivory-colored lower jaw was stretched open, its conical teeth as big as dinner plates.

Stomping on the throttle, I shot away from the monster’s maw a split second before it snapped shut on the Barracuda.

The depths before me were a swirling freeway of converging masses, impossible to track on sonar or see through my night vision.

Operating purely on adrenaline and fear, I executed a tight U-turn and raced back in the direction we had come from, drawing the chaos behind me into an angry pod of Miocene sperm whales. Sonar quickly distinguished parent from calf, and I realized the pinging had disturbed a sleeping nursery. As the cetaceans closed behind me into a protective pod, I dove straight for the bottom, executing a tight barrel roll into a 180-degree turn, slingshotting past the confused behemoths, just missing being swatted by a fluke the size of a garage door.

With nothing but open water ahead of me, I raced over the plateau’s cliff face into the northern basin, feeling giddy over having survived yet another confrontation with death.

“This is Schager. That was some maneuver. Now, if you are through teasing the wildlife, come to course zero-three-seven. The extraction zone is less than six kilometers away.”

Seeking to gauge the ice sheet, I surfaced. The frozen ceiling was sloping closer to the water line, but was still forty feet overhead.

“Schager, the ice is too high to reach.”