On a diving expedition, Briana Devon surfaces to find that her twin sister and their boat have vanished. Faced with exhaustion and a fast-approaching storm, Briana swims to a nearby barrier island, where she is revived by Cole De Roca, who had also taken shelter on the island. Bound to Cole by the harrowing experience, Briana turns to him as she struggles to understand what happened to her sister, her twin, whom she thought she knew.