凯西是一个不受欢迎的高中女生，在同学的生日会上，他们同情凯西所以邀请她过来参加。散场后，凯西和两个女孩克莱尔和玛西亚准备一起坐车回家，但是却在停车场被一个神秘男人弄晕绑架。三个女孩醒来后，发现自己被囚禁在一个灰暗的地下室里，被一个叫做凯文的年轻男人绑架。凯文实际上是一个多重人格患者，他正在接受弗莱彻医生的治疗，但是病情却急转直下，于是他齐总的一个人格绑架了三个女孩。其实凯文有23种人格，并且患有分离性身份识别障碍，但是体内的人格其实出现了分歧，有一个邪恶强壮的人格想要获得身体的主导权。一声弗莱彻发现了这一点，于是来到凯文的家里，但是却正巧碰到了那个邪恶的人格，于是弗莱彻也因此失去了生命。凯西发现凯文有多重人格的秘密，于是想要借他的这一特征逃走

Kathy is an unpopular high school girl, at her classmates' birthday party, they sympathize with Kathy and invite her to come over. After the show, Kathy and two girls, Claire and Marcia, were going to drive home together, but they were stunned and kidnapped by a mysterious man in the parking lot. Three girls wake up to find themselves imprisoned in a gloomy basement, kidnapped by a young man named Kevin. Kevin is actually a multiple personality patient. He was being treated by Dr. Fletcher, but his condition took a turn for the worse, so one of his personalities kidnapped three girls. In fact, Kevin has 23 personalities and suffers from dissociative identity disorder, but the personalities in his body are actually divergent. There is an evil and strong personality who wants to gain dominance of the body. Once Fletcher discovered this, he came to Kevin's house, but happened to meet that evil personality, so Fletcher lost his life because of it. Casey discovers that Kevin has a secret of multiple personalities, so he wants to use his feature to escape