A visit to the apnea world championship becomes the beginning of a personal adventure for James Nestor. Fascinated by the uncompromising nature of this sport, he learns freediving – diving without equipment, using just one breath. From then on, he is drawn deeper into the hidden world of the oceans. In the process, he explores the last secrets of the underwater realm: an incredibly rich habitat with "telepathically" communicating corals, glowing fish, and mysterious giant octopuses. Until he ultimately reaches the absolute limits for both humans and technology. A grand journey of discovery that also leads us back to our roots.