Arthur Rowe, a middle-aged Englishman, happens one day onto a fete in blitz-torn London. In an effort to recapture some spirit of the brighter past, he enters the grounds. While there, he has his fortune told, and the seer tells him the weight of a cake that is to go to the person who guesses the weight correctly. Rowe wins the cake and starts to leave, but the clergyman in charge of the affair tries to get the cake back. Rowe is angered and donates a pound note to the cause and leaves.

Just before the German bombers fly up the Thames to terrorize the city that same night, Rowe has his first visitor in months, a man who rents a room in the same house. The visitor behaves very oddly. When given a piece of cake by Rowe, he crumbles it as if looking for something. Then, while Rowe is out of the room, the man slips something into Rowe’s tea. Rowe returns and smells the peculiar odor of the tea, but before he can say or do anything, a bomb falls, wrecking the house. He regains consciousness to find the house demolished.

Because he has few friends to whom he can turn since he killed his wife in a mercy killing, the worried Rowe goes to a detective agency the next day, where he hires a man named Jones to watch after him and discover why someone wishes to take his life. Rowe then goes to the relief office, which was in charge of the fete at which he won the cake. There he finds a young woman, Anna Hilfe, and her brother Willi in charge of the office. The two say they are Austrian refugees. Willi goes with Rowe to the home of the fortune-teller in an effort to uncover the reason for the attempt on Rowe’s life.

At the fortune-teller’s home, the two men are invited to stay for a séance. During the séance, the man sitting next to Rowe is murdered with Rowe’s knife. With Willi’s aid, Rowe escapes from the house before the police arrive. He goes to an air-raid shelter and there remains through the night. He writes a letter to the police, but before he posts it, he calls Anna, who tells him that “they” are still after him. “They” are supposed to be Nazi agents. Rowe still cannot understand why he is a marked man. Anna agrees to aid Rowe and tells him to send an address where he can be reached.

After talking to her, Rowe calls the detective agency. He then learns that Jones, the man he hired, disappeared and that the head of the agency called the police in on the case. Rowe wanders aimlessly about the city until the afternoon, when he meets a man who asks him to take a valise full of books to a Mr. Travers at a hotel. When Rowe arrives at the hotel, he is escorted to Travers’s room. There he finds Anna waiting for him. In fear of their lives, the two wait for the air raids to begin. They believe that Nazi agents will kill them during the noise and confusion of the raids. Then a bomb falls on the hotel. Rowe awakens in a private nursing home without memories beyond his eighteenth year.

Anna visits him several times in the nursing home, and Rowe falls in love with her during the visits. She will not tell him of his past and claims that the head of the institution, Dr. Forester, wants the recovery to be slow enough to avoid shock. One day, a military officer being treated in the home confides that he saw someone digging on the island in a pond on the grounds. The officer is immediately put into a straitjacket, and Rowe is confined to his room without newspapers or his clothes on the pretext that he suffered a mild relapse.

Convinced that some evil is afoot, Rowe escapes from the room and visits the officer. His visit with the officer confirms his suspicions. Within a few hours, the doctor returns and, extremely angry at Rowe, threatens him, too, with a straitjacket. With the help of an attendant, Rowe escapes and goes to Scotland Yard. He turns himself in as the murderer of the victim at the séance; to his surprise, however, he is told that no one was murdered there. The police turn him over to a counterintelligence agent, who tells Rowe that the murder was a fraud to drive him into hiding and that the nursing home is actually a front for fifth-column activities.

The agent, Rowe, and a man from the hotel where Rowe was injured go to the tailor shop run by the man who supposedly was murdered. During the interview, the tailor places a phone call. After the call is completed, he kills himself. Angry at losing the man before learning any information, the agent tells Rowe that he inadvertently was given a cake containing secret film that was taken by Nazi agents from British documents.

Rowe and the agent then go to the home of the fortune-teller. They fail to find the film there, and they get no information. The last stop of the trip is at the nursing home. There they find the military officer dead, killed by Dr. Forester, who, as Rowe now remembers, was at the fortune-teller’s home on the night of the supposed murder. The doctor is also dead; he was killed by the attendant who helped Rowe to escape.

Without telling the counterintelligence agent, Rowe calls the number he saw the tailor dial. When the call is answered, he finds Anna at the other end. Going to her apartment, Rowe discovers that it is her brother Willi who is the head of the fifth-column ring. With Anna’s help, Rowe almost gets the film. Anna, torn between love for her brother and love for Rowe, allows Willi to escape. Rowe, whose memory is almost complete, follows Willi and regains the film at the railroad station. He returns Willi’s gun to him but with only one bullet in it. Willi then goes to the washroom and kills himself, but not before he reveals the last piece of information that Rowe failed to remember: the fact that Rowe killed his first wife to put her out of pain. Rowe is ready to give the film in his possession to the police. He returns to Anna’s apartment to tell her of her brother’s death and to declare his love to her. Although Rowe drove her brother to his death, Anna pledges her love for him.