A FEW DAYS AFTER OLGA passes, Stanley navigates Idabel, carrying Mierzejewska (who's back for another dive) and me, through the narrow channel to the buoy marking the End of the Line, the ship Stanley sank at 1,400 feet. Water rushes into the open ballast tanks, and we descend.

Stanley doesn't have a GPS (he navigates only with landmarks and a compass), so we follow a buoy line down. The End of the Line is dark, empty, and quiet, a graveyard at midnight, and after circling the rusty heap for a few minutes we waltz off to a colony of coral at 1,250 feet. We buzz some gorgonian sea fans crawling with starfish and a porcupiney crustacean, and the strangest safari of my life continues.

Verticality defines the seascape on the edge of the Cayman Trench. Five-story boulders teeter on the cliff walls around us, evidence that the island is crumbling from below, shedding apartment-building-size chunks of limestone and basalt like a glacier calving icebergs.

At 1,750 feet, Stanley abandons the wall, his primary navigational tool, and steers into emptiness. He's heading for really deep water, where he can avoid what he calls the "ultimate sub booby trap"—a nest of 12 steel lobster traps tied together with floating lines, which sits at around 1,800 feet. If Idabel snags on that, we may never see the surface again.

The submarine gets colder with each descending foot, and we pile on layers of clothing. At 2,070 feet, Stanley blows air into the ballast tanks to slow our descent. "No reason to barrel 100 miles per hour into oblivion," he says. "We'll go slowly." We pass Stanley's maximum test depth, 2,220 feet, a boundary acknowledged only with tense silence.

Stanley gets jumpy, his nervousness bordering on fear. "What was that noise?!" he cries when I flick on my camera. Minutes later, when Mierzejewska rummages through her bag, he repeats the shrill inquiry. After two hours of slow descent, nearly half a mile deep, it's not the most comforting time to see the first chink in Stanley's normally impenetrable armor of confidence.

Life at 2,400 feet is a freak show. A siphonophore jellyfish floats by with hundreds of red tentacles glowing like a medley of fireworks, a behavior meant to attract prey. The sub's nine lights illuminate a red-and-yellow-spotted anglerfish resting in the muck, startled that the lure dangling from its forehead would draw a creature as strange as Idabel. Every five minutes we see another tribute to nature's sense of humor, and finally we bump into a flapjack devilfish, a fleshy orange Creamsicle of an octopus with Dumbo ears. It floats in the water column, arms and web extended like a gelatinous balloon, conserving energy in the food-starved environment by riding the bottom currents.

"I've spent plenty of time at 2,000 feet," Stanley spouts as we rest on a ledge, "and I'm amazed at how much of a difference 400 feet makes in terms of the animal life. Half of the things we are seeing right now I've never seen before. Who knows what we'll see in the next hour."

Unfortunately, our trip is cut short after three and a half hours when one of Idabel's motors breaks. The sub has five others, so the failure is more disappointing than dangerous, but no one's inter­ested in discovering the next casualty. Stanley blows air into the ballast tanks and we streak through the water column inside a giant cannonball. Our world transforms from dark to light, a sunrise time-lapse in real time, and we safely punch through the surface and into a spotless blue afternoon. Idabel limps to shore, where Stanley promptly takes the broken motor apart and begins to solve yet another problem.