The film takes place after the July 7th Incident. A mysterious man in black appears in Shanghai under the Japanese rule. He assassinates the commander and senior generals of the Japanese Army Corps as well as the traitor Hu Fei. The Japanese female spy Yoshiko Kawashima was unable to determine who the mysterious man in black was. In order to reveal the identity of him, she pretended to be the No. 7 intelligence agent.

Guerrilla fighter Lam Suet-fan is in charge of the operation which succeeds in crippling the traitorous activities of Ting Chuen. An infuriated Ting strikes back, swamping the occupied territory with spies and exposes the singer disguise of Lam's comrade Laura who is made his mistress. Through the discreet help from Ting's cousin Sai-kit who goes undercover as the traitor's house guest, a series of offensives are launched, resulting in heavy casualties in the Japanese camp. With pressure mounting on both sides, guerrilla leader Lady Spy No.1 entrusts the mission of bombing Ting's signal tower to Lam who will then lead the troop in retreat. The mission fails, leading to the arrest of Lam and Sai-kit. Laura puts her life at stake in order to accomplish the mission and before she expires, reveals herself to be their leader and names Lam her successor to lead the troop to its stronghold in the north. (Synopsis based on audiovisual materials)