A diamond is stolen in Shanghai and smuggled on a ship to San Francisco while its guards and a federal agent try to find the gem and a murderer.
In Shanghai a large diamond is delivered to the house of Chang and guarded by soldiers Tommy Baldwin (Vinton Haworth) and Joe Dugan (Gordon Jones). During an armed attack a man in a gas mask takes the diamond. Several suspects are found, questioned, and searched. Jane Dunn (Constance Worth) pays Wong $500 for the man's name, but Wong is shot dead before he says it. All seven suspects sail on the Asiatic to San Francisco. Baldwin and Dugan are told to get the diamond back or else. A phone calls warns Jane to get off at Yokohama and not to drink poisoned coffee. Her chocolates kill a dog. Baldwin dances with Jane until she kicks him. Jane finds her room ransacked and shows Captain Williams (Frank M. Thomas) a letter she found to her from the Treasury Department. Jane and the captain find Dugan dead. Jane goes to Baldwin's room and is knocked out by an intruder. Kate Collins (Joyce Compton) invites Baldwin to her room, but he says good-night. In his room Baldwin fights the intruder, who then leaves. Baldwin revives Jane. She tells him she is a federal agent, and he shows her the Buddha charm the intruder dropped.
Baldwin and Jane find Kate poisoned and learn that she worked for an insurance company. Jane tells Baldwin to have the captain round up Dr. Fang Tu (Philip Ahn), Anthony Durand (Leslie Fenton), his valet Harvey (Alec Craig), and the always drunk Philip Burton (Dick Elliott). Jane examines finger-prints on glasses. Jane signs for Kate's radiogram that says the man was with a circus. Jane asks for finger-prints and finds that Baldwin's match; the captain arrests him. Jane visits Baldwin and asks if he loves her. He does, and she kisses him. Jane tells Baldwin that the killer changed the glasses. She asks for help from Durand in searching Kate's things. Durand finds his button, and Jane calls the captain; but Durand proves his coat was being laundered. Jane apologizes and asks Harvey to help her pack, giving him candy. The captain calls Jane that Baldwin was shot. Jane calls Customs and is shot.
At San Francisco Jane is carried off. Customs finds jade in Harvey's bag and searches him. Jane walks in, telling Harvey she found the diamond. Durand comes in with a gun and knocks out the lights. Fang Tu shoots Durand to rescue Jane. On a ship Jane and Baldwin wed after she explains that Harvey swallowed the diamond.
This mystery keeps the audience guessing while hinting that Fang Tu is the culprit. The sexual bantering of Baldwin and Jane enlivens the story.