Hunched over, balancing atop the minisub, he rubs the knot on his head as he looks around. From his vantage atop the Barnacle, he sees they are in a giant torus, a donut-shaped chamber, illuminated by the sub’s emergency lights, the ship’s bow wedged tightly between two curved, seven-foot-high vane-like blades. The beam of his flashlight reveals the upper portion of at least a dozen more of the partition-like objects, all splaying out from a curved centerpiece like multiple fans on a horizontal windmill.

Mick stares at the structure, analyzing his surroundings, the regulator wheezing in his ears as he breathes. I know what this is—it’s a turbine, a giant turbine. We must have been sucked down an inlet shaft. The thrumming sound’s gone. The minisub’s blacking the rotation of the blades, jamming the turbine, clogging the inlet.

Mick climbs down from the Barnacle and steps onto a slick, antiquated metallic surface. What happened to the seawater?

And then he is falling backward, his bare feet slipping out from under him, his right elbow and hip slamming against the hard, slimy surface with a hollow thud. Mick groans in pain, then looks up.

The flashlight’s beam reveals a porous, black, spongelike substance coating the entire central section of the ceiling. Droplets of seawater drip on his head.

Mick crawls to his feet and reaches up, surprised to find the porous material extremely brittle, like Styrofoam, only harder. He removes the knife and hacks at the substance, carving out several chunks of crumbling, chalky rock, drenched in seawater.

Mick pauses. The sound of air racing down a shaft echoes somewhere to his right. He reaches up and grabs on to the top of the metallic partition on his right, shining the flashlight’s beacon along the metallic ceiling.

The sound is coming from a four-foot-wide hollow shaft, situated in the ceiling above the next rotor blade over. Rising at a near-vertical angle, the dark passage appears to lead up through the roof like a bizarre laundry chute.

Mick climbs over the steel wall, then stands beneath the aperture, feeling hot gusts strike his face.

An outlet shaft?

Moving to the next turbine blade, he pulls himself up the barrier and straddles the two-inch-wide ledge, feeling for the edge of the shaft, his hands probing a steep but manageable incline.

Carefully, Mick gropes the ceiling and stands, balancing precariously along the top of the blade as he pulls himself upward into the dark cavity, crawling into the shaft on his belly. Rolling onto his side, he extends his legs out to the opposite side of the four-foot-wide cylinder, his air tank and elbows pressed against the wall to his back. He looks up, the hot wind in his face, his light revealing a vast conduit, rising into the darkness above at a steep, seventy-degree angle.

This is going to be tough …