Liv and Nora, who are cousins, decide to take their families on a cruise. Both have an eleven-year-old and a younger child as well. At one of the ports, the moms take the children out with another family they met on the ship. All goes well until the children, in a brief moment, aren't observed and disappear. From here the nightmare begins, and the story alternates between what is happening to the children and the adults.