年轻女子米歇尔（玛丽·伊丽莎白·温斯特德 Mary Elizabeth Winstead 饰）不久前刚和男友发生争吵，她夜晚驾车奔驰在黑暗的公路上，突然遭遇严重车祸昏迷过去。当她再度醒来时，发现自己被绑住手脚，关在一个密闭的空间里。少顷，一个健硕冷峻的男子霍华德（约翰·古德曼 John Goodman 饰）走了进来。军人出身的霍华德声称地球刚刚遭遇可怕的生化危机，地球人几乎灭亡殆尽。他在数年前未雨绸缪修建了这个设备、资源齐全的避难所，只为生存下去。避难所内，除了霍华德、米歇尔外，还有另外一个年轻男子埃米特。米歇尔对霍华德的说辞半信半疑，她坚信自己遭到了变态狂的拘禁。 　　真相究竟为何？威胁无处不在……After a car accident, Michelle awakens to find herself in a mysterious bunker with two men named Howard and Emmett. Howard offers her a pair of crutches to help her remain mobile with her leg injury sustained from the car crash and tells her to "get good on those" before leaving the bunker. She has been given the information that there has been an alien attack and the outside world is poisoned. However, Howard and Emmett's intentions soon become questionable and Michelle is faced with a question: Is it better in here or out there?