1921

一位无家可归的失忆男子接受一场实验性医学手术，术后醒来发现自己获得新的能力，可以看穿人们内心最深处的伤痛，真实和幻象之间的界线也因而模糊难辨。

黄文展“狗头”（任达华 饰）和何家宝“猪女”（徐子珊 饰）是香港CIB（Criminal Intelligence Bureau）的职员。CIB俗称香港警察中的狗仔队，里面人人行动低调样貌平凡，但却对罪犯有极其灵敏的嗅觉。　　狗头和猪女这次的任务是追踪珠宝劫案的疑犯陈重山（梁家辉 饰）。陈重山是个犯案“天才”，对躲避警察追捕有丰富经验和巧妙手段。这次CIB行动，比平时都更为艰巨。尽管已经警方十面埋伏，狗头和猪女都使出浑身解数，陈重山还是屡屡逃脱。一路的跟踪就好像猫捉老鼠，没完没了。陈重山似乎有神奇的力量，闻到警察追到身边的气味。眼看有警员在追踪过程中殉职，狗头和猪女心急如焚。

A beautiful young woman in the South of France is stalked by, then raped by, a mysterious masked assailant. She shoots him dead soon afterwards and dumps his corpse in the sea. Later, an American investigator turns up, and to her horror he seems to know everything about what she has done......