影片改变自自然主义文学大师左拉的小说《衣冠禽兽》,描写火车司机雅克·朗蒂尔诞生在一个酗酒的家族,他因此总是神思恍惚,以为自己天生是个劣种,一天,他在火车上偶然遭遇了一起谋杀,心有异念的他对警察隐瞒了他看见同事侯保妻子萨维丽娜曾经出现在那个时段的事实,而在此后警方的询问里他一再为他们开脱,这件事让侯保夫妇和他成为了朋友,更出格的是朗蒂尔爱上了萨维丽娜,为了他们能在一起,在萨维丽娜的蛊惑下他甚至差一点谋杀侯保,他的胆怯让侯保逃生,可是,情欲的煎熬又让他无法摆脱和萨维丽娜的关系,但他得知女孩有了新欢,嫉妒使他失去了理智,在一次舞会后他杀了女孩后逃逸,第二天早上,他登上火车,等待他的将是怎样的归宿?!Jacques Lantier is a train engineer who is prone to violent seizures, a condition he attributes to his forefathers' habit of excessive drinking. Roubaud is a train conductor on the same railroad that Lantier works on, married to the much younger Séverine. When Roubaud catches wind of his wife's affair with her godfather, the wealthy M. Grandmorin, he kills him during a train journey in a fit of jealousy. He makes sure that Séverine is also present, making her an accomplice to murder. Lantier, despite having witnessed them quite clearly in the train corridor, hides the fact during the investigation as he is attracted to Séverine. They both begin an affair, all the while Roubaud becomes increasingly withdrawn and starts to gamble. Séverine urges Lantier to kill her husband so that they would be free but she is unaware of Lantier's unfortunate condition.