When HongKong is rocked by multiple gruesome murders, the police forms a task force to investigate. Jun (Sean Lau), once a brilliant detective who suffered a mental breakdown, begins his own investigation. Eventually, the police learn that the murder victims are all suspects of cold cases being rubbed out by a figure known as ‘The Sleuth’. Now, Jun and a detective from the task force are in a race against time to beat the brutal killer at its own game. 电影《神探大战》中，出现了一个以“神探”为名的犯罪团伙，他们以暴制暴、预告杀人、私刑执法，牵扯多重血案，使得香港陷入无尽恐惧之中。同时，患有精神疾病的“癫佬神探”李俊（刘青云饰）独行查案，以“神探夫妇”陈仪（蔡卓妍饰）和方礼信（林峯饰）为首的重案组也身陷与杀戮赛跑的缉凶之路。几方“神探”纠缠在一起，最终结局不知将走向何方。