Captain Frank, a German secret service officer, is shot down and badly wounded on a recon mission on the eastern front. he has to spent several weeks in a field hospital where nurse Maria takes care of him devotedly. When she accompanies him on a train home, Frank proposes to her. They marry in a brief ceremony ans spent a short holiday which is interrupted by a call of Franks officer. He has to return to Berlin immediately, where he receives orders about a very special mission. The High Command is planning a large offensive on the Eastern front and Frank is appointed head of counter-intelligence against Russia. But the Russians are already informed that they are about to be attacked, and have come into posession of the German plans. Head of the Russian intelligence is a certain Sulkin, who so far has escaped any attempt to catch him. Since Sulkin is said to be in Berlin Frank`s main interest is to capture him. His assistents are Captain Weber and comissioner Schulz. Maria has mixed feelings about their visit. She buys some flowers at Jancke where she seems to be a regular customer and where she is treated with great courtesy. Weber and Frank enter the appartement. Maria appears to be somewhat inhibited and Weber wonders where he might know her from. After having diner his worries soon dispeled and the officers retire for a briefing that is overheard by Maria from next door. Suddenly an agitated commissioner Schulz enters anouncing that they have the first traces of Sulkin. Jancke`s flower shop had been turned upside down and certain circumstances indicate that Sulkin might have been there. Maria who listened to his report interrupts her piano playing, shocked. After intensice investigations Weber and Schulz have found out that Maria is somehow connected to Sulkin. But they decide not to tell Frank until they can be certain in order not to ruin his marriage. Weber is close to revealing details about Maria. For this purpose he organizes a friendly get-together at the Marabu-Bar. There, Maria`s brother appears on stage. He has not seen his sister for years because he broke up with her after she told him that she is a spy. This discussion was overheard by some Russian agents and seals the boys fate. Schulz manages to get hold of some juwelry that Maria usually wears. In it he finds a paper with secret letters on it. At the same time Weber discovers that somebody was made a way-proof of his key that belongs to his secret cupboard. He rushes to a telephon booth but before he can call the HQ he is shot by the Russians. Frank who is still at the bar with Maria is informed by Schulz and rushes to the scene of the crime. Maria leaves without being noticed and escaped from the city before somebody can get after her. When Frank discores that his wife is Sulkin he almost suffers a nervous breakdown. But he pulls himself together and asks Col. Seefeld for any difficult mission that will sure mean his death. Meanwhile, under great difficuties Maria has passed the German front lines and has reached the Russians. Though she has brillantly completed her mission she asked to relieve her from service. She suffers from having betrayed Frank and waits for the moment where she put things right again. A Russian colonel who understands why Maria no longer wants to be an agent, tries to win her over by telling her Frank has ordered her brother to be executed. His tactic works. Maria wants to revenge the death of her brother and agrees to work for the intelligence service again. The Russian have occupied Warsaw and plan an advance. Frank, dressed as a Russian captain, arrives In Warsaw. He receives secret material by a colleague. Instead of leaving immediately he accepts an invitation for a ball where he might gain further information. In his fake uniform he has no problem to get into the hall and escapes an arrest. Maria who had been informed of the arrival of a German spy is terrified when she discovers that it is Frank. Stone-cold they face each other. Then they dance. With a few words Frank solves the misunderstanding that he shot her brother. Maria is shocked, in a few minutes Frank will be captured. She fools the Russians who lie in wait, takes Frank to a hidden airport in a general`s car. As he immediately takes off she is shot by the cosacks who followed them, loses control about the car and falls into a chasm.

but under the oberservation of Russian agents