A fabulous jewel known as the 'Dark Star' is stolen; a pastor's daughter gets involved, falling into the depths of a spy plot concerning war plans and fortifications...
Rue Carew, daughter of the America missionary Reverend William Carew, is born in Turkey. According to local belief, she is under the influence of the "Dark Star," an evil planet. It is said that long ago, some metal from this planet fell into the hands of an image-maker, who fashioned the metal into an image of Erlik, Prince of Darkness. "Where you are war is," the image-maker chanted, "and all shall last until you are taken to another land where war shall be." A German secret agent gets hold of the idol, and hollows it out, inserting Turkish plans for fortification he has obtained. He gives the original plans to Carew, with instructions to send them to Germany if he fails to return from the palace of Abdul Hamid, where he has been summoned. But the agent is killed, and during the ensuing uprising, Carew and his daughter sail to America with the idol.
Rue, now a young woman, finds the plans in the idol and shows them to her father. He explains that he did not return them to Germany because he believed they might be used against the United States someday. Rue begins to accept boarders, two of which are Brandes and Stull, who win her good graces but are hatching a plot. Rue spends her time doing housework and engaging in target practice with her pistol. While she is practicing one day, a piece of the target strikes Jim Neeland, an artist and son of a mill owner. Neeland sketches Rue, but they part not expecting to see each other again. When Rue returns home, she finds her father dead on the floor.
The plans become the focus of a worldwide search by the German Secret Service. The chief agents are an adventuress named Princess Naia, and Prince Alak, who is impersonating a Cossack nobleman. Naia meets Neeland and realizes she can use him for her purposes. Rue is about to be married to Brandes when he is exposed as a fraud. She flees to Neeland's studio, where she meets Naia. Naia offers to take Rue home, where she hopes to discover where the plans are. Neeland, who is actually cooperating with the French Secret Service, goes to Rue's house for the plans, and when Rue arrives, he hides. When she produces a suitcase in which the plans are hidden, he takes it from her at gunpoint. Rue informs Naia and Alak that she not only knows the plans from memory, but is also able to reproduce them. When the German agents learn that Neeland is going to sail to Europe, they decide to sail with him, taking Rue along. They put a potion in Neeland's soup, which renders him temporarily unconscious. They then proceed to search his room, to no avail. Rue sees all this and is conflicted. She loves Neeland, but she also loves her country. The search is interrupted by a steward bringing a message to Neeland. Neeland reads the message and explains the truth to Rue. He takes Rue's suitcase to the Captain, who places it in a safe.
Naia and Alak plant a bomb on the ship and tie up Neeland and Rue. They then escape the ship and board a nearby German vessel. Rue manages to free her hands, then takes her revolver and fires it at the bomb. She destroys the timing mechanism, then fires at a water pitcher to put out the flames. The pair are rescued by the ship's officers, and the plans are safely placed into French hands. Naia and Alak shadow the pair, and kidnap Rue. Just as she is about to be killed, Neelan arrives with agents of the French Secret Service. Alak commits suicide by leaping out of a window, and Naia is slain. Rue and Neeland are now safely united in their love.
