A colonial police detective in an Eastern seaport seeks a stolen gem, and infiltrates the underworld by posing as a look-alike wharfside bar owner.

An inspector and detectives Jack Wilson and Yuting meet in Singapore to plan the arrest of Johnny Fly, a jewel thief and murderer. A woman named Edith asks Jack to protect her uncle's ruby from Fly, who later robs him. Yuting is murdered by one of Fly's cohorts. Fly then has Edith kidnapped and tries to force her to reveal the location of the ruby. Eventually, the inspector saves Jack, Edith is rescued and the stolen jewels are recovered.