故事講述香港海關在一次例行海上巡邏中，查獲一艘藏有大批殺傷力武器的貨船，調查過程中遭遇一群海外勢力轟炸搶奪。為追查走私真相，張允南（張學友飾）派出下屬周正禮（謝霆鋒飾）與國際刑警一同遠赴海外，輾轉龐大而複雜的軍火黑市，頂著漫天炮火追查線索的周正禮剛有眉目，噩耗卻突然從香港傳來，原來軍火失竊另有內情......
Hong Kong Customs and Excise Department officers Chow Ching-lai (Nicholas Tse) and Cheung Wan-nam (Jacky Cheung) share a close mentor-student relationship. On a case involving seized smuggled arms, Ching-lai is sent to take part in a joint operation with Interpol to capture a reclusive arms dealer. However, Wan-nam makes a drastic decision that complicates the case even further.