On Valentine’s Day, a double-decker bus explodes in a fiery blast, killing many and leaving charred remains, with evidence pointing to a deliberate act by two passengers, Fai and Ike, a gay couple from troubled backgrounds living on society’s margins. As retired forensic expert Lung Sir investigates, he uncovers their tragic story of abuse, homophobia, and despair, culminating in their decision to end their lives in a suicidal protest against an unjust world, leaving behind a haunting message: “On a beautiful day, we end our unbeautiful lives.”

香港海关在一次例行海上巡逻中，查获一艘藏有大批杀伤力武器的货船，调查过程中遭遇一群海外势力轰炸抢夺。为追查走私真相，张允南（张学友 饰）派出下属周正礼（谢霆锋 饰）与国际刑警一同远赴海外，辗转庞大而复杂的军火黑市，顶着漫天炮火追查线索的周正礼刚有眉目，噩耗却突然从香港传来，原来军火失窃另有隐情……