Chris Lemons (Finn Cole) is a professional diver and still at the beginning of his career. Unlike his fiancée Morag, who is very aware of the risks of the job, he is looking forward to his next assignment far off the coast of Aberdeen, Scotland. His teammates for the planned 28 days at sea are the experienced Duncan (Woody Harrelson) , a father figure to Chris, and the professional but aloof Dave (Simu Liu). No sooner has their escort ship Tharos reached the dive site in the middle of the North Sea than a storm brews that threatens to jeopardize the mission. Nevertheless, the three of them go down over 90 meters with the diving bell. At first everything goes according to plan, but suddenly parts of the ship's system fail, making it necessary to abort the mission. While Dave is able to save himself in the bell, Chris' supply line breaks and he is stranded on the seabed - in icy blackness and with only ten minutes of emergency oxygen. The entire team is unsure whether Chris is still alive, but they do everything they can to save him. With unique solidarity and in a breathless race against time...