接连发生的两起谋杀案让市民们陷入了恐慌之中，犯罪者干净利落的作案手段亦让警方没了头绪。警方好不容易找到了一个嫌疑人，哪知道这名嫌疑人在不久之后亦被杀害，案件彻底的陷入了迷雾之中。焦头烂额的布瑞格斯探长（劳伊德·诺兰 Lloyd Nolan 饰）找到了优秀的探员柯代尔（马克·史蒂文斯 Mark Stevens 饰），希望他能够成为终结这一连串噩梦的那个人。 经过缜密的调查取证，柯代尔发现这一切和一个名为埃里克（理查德·威德马克 Richard Widmark 饰）的男子以及他领导的帮派有着不可分割的联系，于是他隐姓埋名潜伏在帮派内部，哪知道在警方中，亦有帮派的卧底存在。
Plot Summary:After two gang-related killings in "Center City," a suspect (who was framed) is arrested, released on bail...and murdered. Inspector Briggs of the FBI recruits a young agent, Gene Cordell, to go undercover in the shadowy Skid Row area (alias George Manly) as a potential victim of the same racket. Soon, Gene meets Alec Stiles, neurotic mastermind who's "building an organization along scientific lines." Stiles recruits Cordell, whose job becomes a lot more dangerous...
