香港鬧市發生嚴重交通意外，刑事情報科(反恐)警司葉國帆 (吳鎮宇 飾) 和總督察程滔 (張家輝 飾) 逮獲一名女黑客姚可儀 (姜珮瑤 飾)。保安部警司井進賢 (古天樂 飾) 認為葉和程有可疑，向警務處處長要求禁止兩人插手案件。調查範圍擴展到緬甸和西班牙，井和程在多次合作中產生矛盾，在葉眼裡，兩人忠奸難分，處長卻認為葉顛倒黑白，懷疑有神秘組織操控事件，需深入調查。可是，姚可儀口供帶誤導性，警隊高層一時間迷惘，不曉得誰正誰邪…….

A frightening car crash in downtown Hong Kong sparks a war between the local police and the international criminal organizations. Superintendent Yip (Francis Ng) and Inspector Ching (Nick Cheung) from the Criminal Intelligence Bureau (Counter Terrorism) has arrested a female hacker named Yiu involved in the accident. But the two police officers are suspected by Superintendent Cheng (Louis Koo) of the Security Wing. Cheng requests the Commissioner of Police to forbid the two to take part in the investigation. Meanwhile, vital clues led them to the far foreign soil of Myanmar and Spain. Cheng and Ching work together but not hard enough to handle their conflicting ideas. While Yip just can’t trust neither one of them, he himself is being watched by the Commissioner who doubts if Yip is covering up evidences of crimes. The Commissioner believes that there have been moles in their midst and thus, a deep probe into a mysterious gang is needed. While everyone in the Police Force might be a rat, and investigation has gone astray by Yiu’s statements, heads of the department are completely clueless about who is good or evil.

Denzel Washington returns to one of his signature roles in the first sequel of his career. Robert McCall serves an unflinching justice for the exploited and oppressed – but how far will he go when that is someone he loves?