Russian commissar Krotoff orders his best female spy, Vera Marova, whom he calls "Comrade V," to go to Occupied Paris and impersonate Nazi spy Greta Hiller, whom she resembles. As the Gestapo has killed Krotoff's other agents, Krotoff orders Vera to obtain information about Nazi submarines operating off the coast of France. Vera's only identification as a Russian agent is a two-franc piece. In Paris, meanwhile, under orders from Gestapo Colonel Wolfgang Heinrich, Captain Richter reprimands State Police Captain Fritz Kleis for prematurely executing an enemy agent. Vera crosses enemy lines with the help of the French Underground, but when her escort in the country is killed, she escapes to Paris alone. There she meets her contact, artist Henri Devallier, who tells her that the real Greta met with a "terrible accident," and provides her with Greta's cigarette case. Devallier then turns Vera in to Richter and Kleis as an enemy spy, but Heinrich believes she is Greta and arranges lavish quarters for her. When American pilot Steve Worth and English pilot Gerald Naughton are shot down in the countryside outside Paris during a night raid, they are given shelter by farmer Pierre, who advises them to seek out Madame Finchon, a member of the Underground movement, at La Petite Papillon café in Paris. Pierre is killed by German soldiers, and Steve and Gerald escape to Paris, where they split up and agree to meet later at the café. Eluding German police, Steve sneaks in to Vera's apartment while she is entertaining Heinrich, who is enamored of her. Vera hides Steve from the colonel, who tells her that the Germans are planning to destroy an American supply convoy before it can reach Russia. When Greta's suspicious maid Minna reports to Richter and Kleis that "Greta" is not herself, Richter accuses Vera of being an impostor. After Steve knocks Richter out, Vera tells Minna that an assassin has attacked him. Kleis then arrives and sees the closet door move. Kleis fires into the closet and discovers that he has shot Richter, who is in his underwear. Steve, meanwhile, has escaped in Richter's uniform, and Heinrich is so beguiled by Vera that he falls for her story that Kleis defended her against Richter's unwelcome advances. After listening to a public speech by Adolf Hitler, Vera sends a secret message about the doomed American convoy to Henri, who reports to a Dr. Suchevsky in the back room of the café. Suchevsky then wires the news to Russia. That night, Steve, disguised in a German uniform, escorts Vera home in order to warn her that she is being followed by the Gestapo. The next day, Kleis obtains Vera's two-franc piece and finds Greta's body entombed behind the fireplace in Henri's apartment. Steve helps Vera slip away from Heinrich and they return to the café. There Kleis and his soldiers attempt to arrest Steve and Vera, but Gerald helps Steve fight off the Germans. Everyone does their part to ensure that Suchevsky is able to wire the new information that Vera obtained from Heinrich to Russia. Suchevsky, however, insists that they escape through a secret passage, and is killed as he transmits the last bit of information. The message reaches the American convoy in time for them to fend off the surprise attack, and the German forces are turned back. Heinrich is executed for revealing military secrets to a spy, while Vera, dressed as a peasant, escapes unharmed to the country with Steve.