The horizon of water sandwiched between the bottom of the ice sheet and East Antarctica’s ancient geology was changing rapidly, the dark silt below yielding to patches of brown sea grass, the width of the passage narrowing quickly, forcing me to reduce our speed. Once placid waters became a minefield of eddies, each invisible swirl of current threatening to drive the Manta into the ice sheet.

Jonas awoke on our second collision, the submersible pilot disturbed to find our passage reduced to a ten- to twelve-foot-wide divide. “Where are we?”

“We’re nearing the glacial basin, the very beginning of the ice shelf. The subglacial river’s close. You can hear it on sonar.”

Jonas took over command. Guided by sonar, he directed us farther to the south.

We felt the river before we saw it, the current pelting us with watermelon-size ice cubes too clear to see and too numerous to dodge. Fifteen million years ago, the waterway had been as wide as the Amazon, twisting across East Antarctica to empty into the enormous delta now occupied by the ice shelf. We only realized the extent of the river’s boundaries when Jonas dived the sub to escape the current and found that the bottom had dropped nearly one hundred feet.

Hazards were everywhere. The riverbed was littered with vortex-channeling boulders and petrified tree trunks as wide as redwoods. Chunks of ice gouged out of the bottom of the ice sheet soared past us like miniature comets.

“Activate the sonar, Zach.”

I pinged, sending sound waves reflecting off objects both stationary and propelled by the current. It was impossible, similar to driving a racecar down a crowded speedway—the wrong way.

Then a different blip appeared on sonar, and I knew this one was going to be trouble.

37

“I am the captain of my soul.”

—William Ernest Henley

Jonas read the incoming data as it crawled across his sonar screen. “Range: twelve kilometers and closing. Still too far out to gauge its size, but it’s way too quiet to be that other sub. Maybe it’s an alien vessel, come to collect you and save me the trip.”

“Jonas, I think it might be a life-form.”

“A life-form? Come on. What kind of life-form could survive down here?”

“Vostok’s rich in geothermal vents. There’s a thriving food chain that dates back to the Miocene. How close do we need to be to get a size reading?”

“On a biologic? Less than six kilometers. What are you afraid of, Zachary? Don’t tell me a Meg—”

“It’s not a megalodon.” I tapped my index finger repeatedly on the sonar REFRESH button until new data scrolled across the monitor.

RANGE TO TARGET: 5.78 KILOMETERS.

TARGET SPEED: 8.3 KNOTS.

TARGET SIZE: 18.89 METERS

TARGET COURSE: INTERCEPT!

Jonas swore. “The damn thing’s over sixty feet long, and it’s headed straight for us. Speak to me, Wallace. What’s out there?”