Kevin, a young man with dissociative identity disorder, harbors 23 distinct personalities within him, each with its own perspective on the world and agenda. When he kidnaps three teenagers—Casey, Claire, and Marcia—the girls find themselves trapped in a dark and mysterious place, where each of Kevin's identities manifests in terrifying ways. As the girls try to escape, they must confront not only the cage they are locked in but also Kevin's personalities, which range from an innocent child to a monstrous manipulator called "The Beast."