Marion Beaumont and her younger sister, Gwendolin, are orphans, inheriting from their father a mortgaged estate, gambling instincts and a social position to uphold. Through gambling and card debts they become deeply involved. Marion gets into the hands of Noel Ferrers, who, under the pretense of helping her, is gradually drawing her into a web of serious trouble, so that he can compel her younger sister, Gwen, to become his wife. Ferrers persuades Marion, in a fit of desperation, to show a magnificent tiara of precious stones lent to her by Madame D'Orville, to Morris, a society pawnbroker. The clever strategy suggested by Ferrers to raise money on the tiara, is to change the box containing the jewel for one which only holds a paperweight. With the money obtained on this, Ferrers tells her her fortune is certain by backing his horse for a race the next day. The horse loses, as Ferrers intends, and Marion is distracted. One night Morris sees Madame D'Orville wearing the tiara which is supposed to be locked in his safe. As the tiara is far too uncommon to be duplicated, Morris sends for Marion and insists upon having the box, supposed to contain the tiara, opened before his attorney the next day. To prevent Morris finding out her deception, Marion drugs and robs him of the fraudulent box. Captain Dorian March, an officer of the United States Army and sweetheart of Gwen's, comes to her rescue. While the police are pursuing Marion, Dorian, although he has no knowledge of what it contains, takes the box and the suspicion with him. After eluding the police by jumping into the river, Dorian enlists as a private soldier in a Canadian regiment. The troopship on which he leaves for the front is torpedoed and sinks with all on board. Gwen is being forced into a marriage with Ferrers, who threatens to expose her sister. She believes Dorian is drowned. The situation is saved by Dorian, who is rescued by a tramp steamer and returns in the nick of time. Also Madame D'Orville learns the true state of affairs, she returns her tiara to the pawnbroker as if from a repentant crook. She is aided in this by a faithful friend of Dorian's and sweetheart of her own, called Hogg, who, in Marion's name, redeems the tiara from Morris. Ferrers' attempt to force Gwen into immediate marriage, to save Marion from the police, is frustrated by Dorian's arrival and the coming of the detective, who tells of the restoration of the tiara to Morris. Dorian is cleared. Marion's honor is saved and Gwen and Dorian are united.