A few days after Christmas, half-sisters Ida and Tuva set out on a winter dive in a remote part of the Norwegian coastline. Toward the end of the dive, a rockslide traps Tuva underwater. As Ida surfaces to call for help, she discovers that the rockslide has struck above water as well, burying their equipment, phones, and car keys; they are completely cut off from any chance of outside rescue. As the frantic race for survival unfolds, Ida is put to the ultimate test of character and forcefulness.