某疯狂科学家（乔宏 饰）因儿子感染艾滋病死亡而精神失常，他命令助手四处绑架同性恋者带到私人货柜船龙宝号上进行活体实验。警局督察长发叔（曹达华 饰）先后派人数次登船搜集证据，最后皆以失败告终。在夜总会演杂耍的石罅米（石天 饰）自幼研习武功，成年后进入特种大队，却因被指控有虐待倾向而离开警队，永不叙用。如今他独自抚养三个孩子，生活倒也快乐。某晚演出时，他和好友老虎仔（林振康 饰）目睹并插手一起绑架事件。由此将麻烦引到自己身上，而另一方面，发叔发现石罅米和一与疯狂科学家有勾结的日本人容貌相似，遂拟定了一个计划……

Professor Kiu is a mad scientist who developed mental disorders from grieving the death of his son. Kiu orders his assistants to kidnap men to his lab, located in a private container on a vessel, for experiments. Police inspector Uncle Wah had sent his subordinates to gather evidence in the vessel, but failed to find any. Shek La-mai, an acrobatic performer and a former commander of the Special Duties Unit is a single father of three children. One night during a performance with his protege, Lam Hong, witnessed and intervened in a kidnapping incident by Kiu's henchmen, and the two became targets of Kiu. On the other hand, Uncle Wah discovers Shek's resemblance to a Japanese scientist named Toyota, who colluded with Kiu. Wah formulates a plan for Shek to act undercover as Toyota in order to gather evidence from Kiu's lab.