London special agents Wong Tak-fat and Fong Lung have arrived in Hong Kong to investigate a murder in connection with a drugs trafficking ring. Fong attends a ball hosted by his girlfriend's rich father Sze Kam-wing where evidences lead him to the Black Eye Bar. Wong befriends the recently widowed bar owner Lee Mei-chen and soon becomes enlisted as member of the ring and the ring leader's trusted aide. Falling in love with Lee, Wong is told that her husband was killed for leaving the organisation. Wong is however unable to establish contact with Fong with all outside communication cut off. Anxious to hear from Wong, Fong investigates discreetly at the bar. Mistaken for a cop, Fong is captured but helped to flee by Lee. Alarmed by Fong's escape and the leak of Wong's identity, ring members are just about to execute Wong and Lee just when the police raid the drugs den and arrest the ringleader—Sze.