In 1935, United States Narcotics Agent Michael Barrows, Dick Powell, is assigned to track a freighter suspected of drug smuggling. When he and the Coast Guard spot the vessel off the California coast, the crew captain murders about a hundred chained laborers by throwing them overboard to drown, a brutal sight that leaves Barrows shaken. The ship slips beyond the 12-mile limit into international waters, escaping pursuit. Fueled by horror and a fierce resolve, Barrows vows to take down the narcotics ring—no matter how far he has to go—without waiting for the okay from his boss, Commissioner H. J. Anslinger, Harry J. Anslinger.
The trail leads to Shanghai, where his Chinese counterpart, Commissioner Lum Chi Chow, Vladimir Sokoloff, has obtained information from a dying man who had escaped a slave-labor camp growing poppies in Egypt. Chow suspects Nicholas Sokim, Ludwig Donath, though Sokim claims he’s been out of the drug trade for years. In Shanghai, Barrows meets Ann Grant Signe Hasso, a recent widow who is preparing to send an orphan Chinese girl, Shu Pan Wu, Maylia Fong, to safety in the United States. A hidden drug-processing lab is discovered beneath Sokim’s business, and Sokim ultimately takes his own life when the truth closes in.
With time running out and the lead growing cold, Barrows travels to Egypt to pursue the hidden poppy fields. There he joins forces with British Commissioner Lionel Hadley (uncredited) and French Commissioner Lariesier, Marcel Journet. They locate the fields on land owned by Binda Sha, Fritz Leiber. Barrows learns the irrigation system for the fields was set up by Ann Grant’s late engineer husband, tying the case closer to the vulnerable woman he’s begun to trust. When Binda Sha realizes he’s been exposed, he leaps to his death from a cliff.
Meanwhile, the narcotics are being smuggled to Beirut in the stomachs of camels. The camels are slaughtered, the drugs retrieved, and an alert agent spots the operation as they are transferred into seemingly innocent butter containers aboard a ship bound for New York via Havana, overseen by Naftalie Vrandstadter, Ivan Triesault (uncredited). Barrows boards the ship and again crosses paths with Ann Grant and Shu Pan Wu, who seems to have developed a schoolgirl crush on him.
As the vessel nears New York, the drugs mysteriously disappear beneath the cover of a fire, though Barrows suspects a clever ploy: the ropes binding the weight-laden packages were treated to part at a precise moment, allowing the contraband to surface undetected. The Coast Guard is alerted, and they capture the drug ring’s boat, recovering the packages. Barrows carries the seized evidence ashore with Ann Grant and Shu Pan Wu. Yet the story twists at the end: Shu Pan Wu steals a revolver and orders the crew to steer away, only to reveal that the gun is loaded with blanks. The revelation crushes Barrows’ assumptions as Shu Pan Wu turns out to be the adult mastermind behind the operation, a startling twist that underscores how far-reaching the narcotics network really was.
