Nia would do anything to win the approval of her boyfriend Scott and his friends, especially mean girl Olivia. When Olivia dares Nia to explore an abandoned prison, she sees it as the perfect opportunity to prove herself. Facing dark tunnels, distant noises and creepy mementoes left behind by incarcerated criminals will surely all be worth it. But it isn't long before Nia and her little sister, Kayla, find themselves trapped inside. And then Kayla vanishes. Suddenly, this feels like more than a game gone wrong. Someone is hellbent on making Nia and Kayla the prison's last inmates.