The Huautla in Mexico is the deepest cave in the Western Hemisphere, possibly the world. Shafts reach skyscraper-depths, caverns are stadium-sized, and sudden floods can drown divers in an instant. With a two-decade obsession, William Stone and his 44-member team entered the sinkhole at Sotano de San Augustin. The first camp settled 2,328 feet below ground in a cavern where headlamps couldn't even illuminate the walls and ceiling. The second camp teetered precariously above an underground canyon where two subterranean rivers collided. But beyond that lay the unknown territory -- a flooded corridor that had blocked all previous comers, claimed a diver's life, and drove the rest of the team back. Except for William Stone and Barbara am Ende, who forged on for 18 more days, with no hope of rescue, to set the record for the deepest cave dive in the Western Hemisphere.