Inspector Cheng Ao-Chun, a Taiwan sharpshooter, is on a mission to investigate an underground arsenal on Hai Han Island in Hong Kong. As it has been regarded as a base of coordinating all arms deals, public security officer Hua Chun Yung, a nimble fighter from China, is on the same mission. Thus, the two become undercover agents inside the syndicate. In one arms deal, Cheng and Hua have their identity exposed by Hong Kong inspector Yeung. Despite the Hong Kong government authorities' wish to repatriate them, the two insist on staying on security grounds. Hong Kong government submits but has asked Yeung to spy on their movements secretly in the territory. However, the three with different backgrounds confront against each other. Hua gets acquainted and falls in love with Edna, who is the sister of ringleader Marco. On the other hand, Hua tries to trap Marco through their relationship. Marco is eventually arrested during a fight with Yeung. The four are in deep emotion, as Yeung and Edna see Cheng and Hua off on their homeward journey.