The dramatic and action-packed story of the last mysterious place on earth—the world’s seafloor—and the deep-sea divers, ocean mappers, marine biologists, entrepreneurs, and adventurers involved in the historic push to chart it, as well as the opportunities, challenges, and perils this exploration holds now and for the future. “Should be required reading. . . . A gripping and all-too-timely account of what in more ways than one is turning out to be a very costly and questionably necessary race to the bottom. . . . Trethewey rises to the occasion here, relating in absorbing detail the ebb and flow of conflicting interests that tussle down among the vents and ridges of the hadal zone. It is all highly readable, and it is all deeply ominous.”—Simon Winchester, New York Times Book Review