While on assignment in Greece, journalist James Nestor witnessed something that confounded him: a man diving 300 feet below the ocean’s surface on a single breath of air and returning four minutes later, unharmed and smiling. This man was a freediver, and his amphibious abilities inspired Nestor to seek out the secrets of this little-known discipline. In Deep, Nestor embeds with a gang of extreme athletes and renegade researchers who are transforming...