Spy No. 13.

During World War II, spy Wu Lai-sheung is instructed by her superior Fan Yeung-shan to murder spy number 13 Cheung Chi-ping. While Wu establishes a relationship with Sakei, the assistant general of the Japanese army, she also gets acquainted with Cheung. Cheung and Wu fall in love. Wu recommends Cheung to become Sakei's driver. Cheung pretends to court the Japanese spy Siu-kuen, but Siu-kuen arranges to kill the spies contacting with him. Cheung has seen through Kuen's identity for long. When Kuen is going to kill Wu, Cheung kills Kuen, Fan compels Wu to kill Cheung. Wu follows the instruction to murder Cheung. After the murder, Wu disappears. After the war, Fan discovers Wu ends up in asylum. When he visits Wu, he tells her of Cheung's innocence. This breaks Wu's heart. Cheung turns out to have seen through Wu's identity for a long time and pretended to have been killed to cover up his identity and facilitate his work. With the truth known and the war ended, Cheung and Wu married.