Marie is kidnapped and taken aboard ship, then thrown off at Yucatan. She winds up singing in a cafe in the Panama Canal zone. There she gets involved in a plot to destroy the canal and runs into American intelligence officer Crawbett.

In a seacoast town in France, Marie Galante, a telegram messenger, delivers a message to an American captain ordering him to pick up additional crew members and a special cargo before a rendezvous at the Panama Canal in six months. The telegram is signed "Ryner." The drunken captain invites the pretty Marie onto the ship to take down his reply, and when the ship leaves port, he reports her as a stowaway and locks her in a room. In a seacoast town in Central America, Marie, who has escaped, is told that the only place she can board a boat for France is at the Panama Canal. There, Ratcliff of British Intelligence meets with General Phillips, in charge of the Zone, concerning two suspicious men: General Saki Tenoki, a retired Japanese officer, now a dealer in curios; and Ryner, who plans to damage the canal as the U.S. fleet passes through it. The only thing they know about Ryner is that he always works through a woman and that the woman is always mysteriously killed. After Phillips introduces Ratcliff to Dr. Crawbett, an American studying tropical diseases, Ratcliff, suspicious of him, invites him to dinner, and they go to the Pacific Gardens, where Marie sings. Tenoki is at the club, and he shows interest in Marie, as does a man who gazes at her intently, named Brogard, who runs a Parisian bazaar near Tenoki's curio shop. Hoping to get help to return to France, Marie visits Brogard's ship, and he offers to get her a ticket if she finds out from American Navy officers when the fleet will leave. He says he needs to know to be able to have a jump on his competitors in ordering merchandise for the officers, and Marie naïvely agrees. Crawbett, really an American secret service man, intercepts a message from Tenoki asking Marie to meet him at his shop at night. After Tenoki's clerk, who sent the message, is found murdered, Crawbett has Washington officials make inquiries about Ratcliff, Tenoki and Marie. Marie visits Tenoki's shop in the rain, and he insists that she change into a kimono. He then questions her about the old French dredges built sixty years ago where his servant was killed and offers to help get her home if she'll find out secret information concerning the dredges from Brogard. After Crawbett sees Maria leave wearing the kimono, he questions her and angrily calls her "anybody's woman." Upset, she goes to pray in a nearby church, and when Crawbett sees her kneeling angelically before the Virgin Mary, he apologizes and promises to get her home if she refuses to see Brogard or Tenoki again. However, when word comes from Washington that Marie is a stowaway, and the ship that she was on arrives at the canal, the governor-general tells Crawbett that she must remain. Brogard plans to have the foreman of the canal's powerhouse, who looks like him, kidnapped so that he can replace him when the fleet comes through. After Crawbett informs Marie that she must remain until the mystery is cleared up, she returns to Brogard, who offers her passage to France if she will deliver a message to Tenoki. At the French dredges, Crawbett, with Ratcliff, finds dynamite in a pit at the location where the body of Tenoki's clerk was found and surmises that the dynamite has been brought by the ship and will be used to put the powerhouse out of commission and thus stop the canal. Crawbett brings Tenoki to the pit, and they find Ratcliff murdered and the dynamite gone. Before the governor-general, Tenoki admits that he is an active officer of the Imperial Japanese Navy sent to find Ryner, who is paid to start wars by individuals who stand to profit. That night, Crawbett finds Brogard, who is really Ryner, at the powerhouse, and as they struggle, Brogard shoots Marie before Crawbett shoots Brogard. The ships pass unharmed, and both Crawbett and Tenoki visit Marie in the hospital and plan to go with her to Paris.