Wu Fang rules the Chinese underworld with the aid of crooked politician Jim Murdock, who shields the criminal from the police in exchange for a share of the profits. When Wu Fang kills Sergt. Joe Duncan, however, Patrolman Terence Shannon decides to conduct a raid. Wu Fang, who is expecting to receive a large shipment of opium, kidnaps Chinatown mission worker Patsy O'Connell and threatens to harm her if the police interfere in the drug smuggling operation. Although Terence is attracted to Patsy, he places duty before his own feelings and goes ahead with the raid but is captured by Wu Fang. Patsy and Terence are about to be thrown into a rat-infested pit when Officer Michael O'Shea and his men arrive, and in the ensuing battle, Wu Fang is killed and Murdock arrested. Chinatown having been made safe, Patsy agrees to be the wife of the new police chief, Terence.