In the year 1935, following a United Nations-sponsored meeting of the World Narcotics Commission, the U.S. Treasury Department, Bureau of Narcotics undertakes a crackdown on the worldwide opium trade. Assigned to the investigation is Treasury Department agent Mike Barrows, who is head of the department's San Francisco bureau. Mike is familiar with the ruthless ways of the drug traffickers, having witnessed an unmarked Japanese freighter jettison one hundred Chinese slaves off the San Francisco coast to gain enough speed to outrun a U.S. Coast Guard patrol. A life preserver bearing the name Kira Maru , and a view of the offending captain, as seen through binoculars, are the only clues Mike has to go on as he begins his investigation in Shanghai. There the captain of the ship is tried in absentia and is sentenced to only thirty days in prison if found, angering Mike. Following Mike out of the courtroom is Lum Chi Chow, the Chinese Commissioner of Narcotics, who later plays a recording for Mike of a man talking about the Kira Maru and the 200 slaves it transported to Egypt to plant poppies. Although the exact location of the Egyptian poppy field is unknown to investigators, Lum believes that it will be learned when the flowers are harvested, which must occur five days after the petals fall. Later, while searching notorious drug dealer Nicolas Sokim's rickshaw garage, Mike meets Ann Grant, the widow of an American engineer, who is about to send her young Chinese ward, Shu Pan Wu, to San Francisco. After Sokim fails in his attempt to throw Mike off his trail, he kills himself by ingesting poison. As it is unlikely that the drugs will reach Shanghai now that Sokim, the Chinese contact man, is dead, Lum sends Mike to Egypt, where the poppies are now ready for harvest. There Mike discovers a trail of evidence pointing to Ann's complicity in the elaborate drug smuggling operation. The already harvested opium, it is learned, is being transported across the desert in a camel caravan to Beirut, with $1,000,000 in narcotics hidden in the stomachs of the camels. Mike follows the packages containing the drugs to Havana, where the opium is to be refined before it is sent to the United States. Ann's connection with the smuggling operation appears certain when Mike discovers her and Shu Pan in Havana, but he decides to follow the drugs to their final destination before making any arrests. After watching the opium, which is now packed into butter cartons, being loaded onto a ship, Mike boards the ship for the journey to New York. En route, a fire is set in the ship's galley as a diversion, and the packages containing the drugs are thrown overboard with weights attached to them. When Mike discovers evidence that the drugs were ejected from the ship, he notifies the U.S. Coast Guard, which sends a patrol boat out to meet the ship. Mike forces Ann and Shu Pan to accompany him to the dumping site, where they discover a fishing boat already there to pick up the drugs. A gun battle ensues, during which Shu Pan makes a grab for Mike's gun, thereby revealing herself to be the head of the drug smuggling ring. The revelation does not surprise Mike, however, who has known the truth about Shu Pan ever since he witnessed her strange behavior during the shipboard fire. As Mike anticipated that Shu Pan would grab his gun, he loaded it with blanks, thus foiling her attempts to shoot him. With Shu Pan's arrest, Mike brings to an end a worldwide drug smuggling operation.