Thirteenth birthdays are a good occasion for cake, presents, and demonic rituals in Olivia's case. When she and her friends accidentally open a gateway, they unknowingly call through a demonic entity hell-bent on terrorizing them one by one. When their shared trauma drives a wedge in their friendship, they feel the distance grow between them but unable, or unwilling, to stop it. Fifteen years later, they must join together again to rid themselves of the horror they brought into this world, for fear of their sanity and their lives.