I was about to retort when a flesh-tingling zzzzzzzzzzt sound rattled the cockpit’s dome. My stomach knotted. “I think I just screwed the pooch.”

“What was that sound?”

“We were just echolocated. Ben, kill the engine.”

“Damnit.” Ben powered down the propulsors, allowing the neutrally buoyant sub to rise slowly to the surface.

“This is Colonel Vacendak. Why have you stopped?”

“We were just echolocated by a biologic, a Miocene sperm whale.”

“Wait… that fossil we saw?”

“Easy, Ben. So far it’s staying deep.”

“But we’re not. The moment we hit the surface, the river’s current will carry us east again.”

“Dr. Wallace, the biologic is circling between you and the entrance to the bay.”

“Thank you, Colonel, we know.”

“We suggest you wait until you get closer and then accelerate past it into the bay. We can guide you into the shallows where you’ll be safe.”

I turned and looked at Ben and Ming. “It’s worth a shot.”

The Barracuda continued to rise. As it drew closer to the surface the current swept us up and carried us east at seven knots.

Another tingling zzzzzzzzzzt rattled the sub.

I listened intently on sonar. “Damn. It’s either feeding along the bottom or waiting in ambush. I can’t tell which. Twelve hundred feet until we pass over it. Hang tight, Ben.”

“Captain Hintzmann, once you’re in the bay, relinquish command and we’ll remotely guide you to your destination. No worries; we’ll see you past this little speed bump.”

“Obviously you didn’t see the size of the little speed bump’s teeth. Zach?”

“Stand by. Eight hundred feet.”

Zzzzzzzzzzzzzt.

I heard Ming cry out in the darkness.

“Three hundred feet. It’s gotta know we’re here. Ben, restart the engine but don’t hit the gas until I say.”

“Just keep in mind this monster probably has another gear, too.”

“Two hundred feet. It’s getting agitated… It just went vertical. Shit, it’s fast. Gun it!”

I clenched my teeth and cursed myself as the propeller struggled to catch water a second before the back of my head hit the seat and we shot ahead—

—the surface behind us erupting.

I turned to see a white lower jaw and abdomen rise majestically from the depths.

Livyatan melvillei… This is insane.

For a spellbound moment the hundred-ton bull whale seemed to defy gravity. Then it collapsed belly-first in the water, its tidal-wave splash crashing over our acrylic cockpit. By the time the creature attempted to echolocate us again, we had entered the tributary doing thirty knots.

Ben continued on a northerly course for another three miles before he was convinced we were sufficiently safe enough to warrant turning the sub over to Vostok Command.

“It’s all yours, Colonel.”

I grabbed for the handrail as the Barracuda rolled into a steep dive, avoiding islands of ice. We accelerated through the depths, our sonar now thankfully biologic-free.