John Cranford is a U.S. customs agent dedicated to stem the activities of a gang of opium smugglers. After successfully closing the case, Cranford takes a vacation on Pidgin Island, near Kingston, Ontario. Here he meets the beautiful Diana Wynne, whose mysterious behavior both fascinates and attracts him. It turns out that Diana is herself a secret service agent, bent on trapping notorious pearl smuggler Michael Smeed.

U.S. Navy Lieutenant George Blenton becomes drunk at an official reception, and his fiancee, Jane Ravenslee, the captain's daughter, breaks their engagement. After war is declared, George, entrusted with a secret code book to deliver to an English admiral, drinks and loses the book which German spies recover. During a private court-martial he is offered a pistol for suicide. After drinking again, he fires a shot, but still lives. Put ashore on the island of Tafofu "to rot," George, hating the U.S., moves in with Lehua, a half-white who tries to wean him from drink.

At a London auction, Princess Sonia bids against her husband, exiled Prince Victor, for a Corot landscape in which incriminating letters Sonia wrote are hidden, but it is bought by Michael Lanyard, suspected of being the mysterious, international thief "The Lone Wolf." After Lanyard gives Sonia the letters, she divorces Victor, marries Lanyard and dies after bearing their daughter Sonia. Years later, Sonia, who thinks she is the daughter of the Princess' maid, is found by Victor, now the leader of an underworld gang of Oriental crooks and Bolsheviks. Saying he is her father, Victor brings her to his home, hoping to entice Lanyard to make an appearance.

Dr. Spencer's wife becomes intensely jealous when she finds, in her husband's coat, a note signed "Mary," which asks him to visit the writer at the Hotel Mum. The woman carries her tale of woe to Attorney Thomas, a family friend. In his effort to make light of the matter, Thomas soothingly places his arm about Mrs. Spencer's shoulder. Dr. Spencer's office is directly across the court. Glancing out of the window, the doctor sees his wife apparently being embraced by Thomas. The attorney consents to accompany Mrs. Spencer to the Mum and meet "Mary." The doctor trails the two. As luck would have it, Mrs. Thomas passes the Mum just as her husband and Mrs. Spencer enter. The doctor and Mrs. Thomas meet and make their way after their other halves, bent on vengeance bent.