This film portrays the final days of the famous Dutch erotic dancer, who was executed by the French for spying on October 15, 1917.
Three traitors and spies are shot by firing squad, one (Mischa Auer) refusing to name Mata Hari. The first flight from Russia over German lines brings dispatches to Russian general Shubin (Lionel Barrymore) in Paris. Mata Hari (Greta Garbo) dances for the god Shiva at a high society party. Andriani (Lewis Stone) is working for the Germans and tells Mata Hari to see Shubin that night. While Mata is gambling, the Russian pilot Alexis Rosanoff (Ramon Novarro) buys a ring and gives it to her. He takes her home and brings her flowers the next day, but she calls him a fool. Dubois (C. Henry Gordon) warns Shubin that Mata Hari is a spy, but he needs proof. Mata Hari says that everyone knows she is a spy. Shubin fears he has lost his honor.
Rosanoff is given dispatches to take to the prime minister in Petrograd. He says good-bye to Mata Hari, and Shubin reprimands him jealously. Mata Hari sends a message to Andriani and visits Rosanoff, who says he loves God, country, honor, and Mata Hari. She asks to be first and insists he put out a sacred candle. In the dark Andriani's man steals the dispatches. Andriani orders Carlotta (Karen Morley) out of Paris; she threatens to tell the French police and is soon eliminated. Andriani commends Mata Hari's obedience and gives her photos of the dispatches to send to Holland by way of Shubin. She says Rosanoff wants to marry her, and Andriani warns her that a spy in love is of no more use. She says she does not want to see Rosanoff again.
Dubois tells Shubin that Mata Hari went to Rosanoff. Shubin breaks his mirror and jealously calls Mata Hari a liar. She gives him the photos, but he calls Dubois to tell him that she is a spy. Shubin says Rosanoff is a traitor and calls the Russian embassy; Mata Hari tries to stop him and then shoots him. She puts the gun by his hand and recovers the photos. Rosanoff comes in, and she tells him to forget her. As Dubois is arriving, she locks the doors and goes out.
Rosanoff takes off in a plane. Mata Hari reminds Andriani the papers reported Shubin's death a suicide. He says Rosanoff was in a plane crash, and she resigns. He observes the only way a spy can resign is by dying. Mata Hari visits the blind Rosanoff in a hospital; he wants to marry her. She escapes Andriani's assassin but is arrested, tried, and convicted of espionage. She says good-bye to Rosanoff, pretending she is having an operation before going to the firing squad.
The real Mata Hari claimed she was spying on the Germans, and the French have refused to reveal the evidence. Mata Hari is notorious for using her sexuality to spy; the film leaves little doubt she betrayed the Russians and French. Such intrigues are also casualties of war.