: Former intelligence workers, husband and wife, are involved in a secret operation and expose a group of spies.

Spring of 1940. Former intelligence agents, spouses Birsford, Tommy and Prudence (whose family name is Tuppence), worry that they are not enlisted in the army because of age, and they want to be useful to the country in difficult times. The conversation of the spouses is interrupted by the arrival of the chief of the Secret Service, Mr. Grant. Tuppence comes out briefly to bring the guest a treat.

Mr. Grant can offer Tommy only boring paper work, but at this time, Tuppence's friend calls and asks her to come urgently.

Left alone with Tommy, the boss offers him a job. The special services became aware that two of the people in senior positions are traitors. The agent who tracked them down died before pronouncing "N. or M., Song Susie. " It is known that M. is a woman, N. is a man, Song-Susi is San Susi, one of the guesthouses in a small Scottish resort town, where old ladies, old maids and retired military men usually stay. Grant invites Tommy to continue the work begun by the deceased.

Burning with impatience, Tuppence Tommy says that he is going to the wilds of Scotland to perform a boring and uninteresting job, which, unfortunately, he cannot take with him.

A few days later, Tommy, under the name of Mr. Meadows, a widower, arrives at the guesthouse. The hostess of the guesthouse, Mrs. Perenna, introduces the new guest to the tenants. Among them are a huge growth lady Mrs. O`Rork, Major Bletchley, a young man Carl von Deining, an old maid Miss Minton, an elderly couple Mr. and Mrs. Cayley, Mrs. Sprot with her little daughter Betty and Mrs. Blenkensop, under which his wife Tuppence was disguised.

Having found Tuppence alone, Tommy asks how she got here. Seeing Mr. Grant, Tuppence immediately realized that he had come for a reason. She immediately left the room, called her friend and asked her to call her back. Saying that she was leaving, Tuppence hid and heard everything. Now the couple will work together. Tuppence, who pretends to be the widow who buried her second husband, will chase Tommy.

Spouses study guests, but find nothing remarkable. Their attention so far has been attracted only by Karl von Deining, a German hiding in Scotland, whose entire family died in a concentration camp. He surprisingly speaks poorly of the English. Tuppence notices that he is interested in the daughter of Mrs. Perenna Sheila. The remaining inhabitants of the guesthouse conduct meaningless conversations about the war, worrying about their loved ones who are now at the front. All is taken by baby Betty. The girl’s favorite game is to hide a toy dog ​​named Bonzo. Mrs. Sprot constantly asks one of the inhabitants to look after the girl.

Major Bletchley is delighted to see Tommy; he will now have someone to play golf with. They are joined by Captain Haydock, a nearby retired naval officer who now heads the local defense. The captain also joyfully greets Tommy and invites him to visit his villa.

In a designated place, Tommy meets with Grant. Learning of the tricks that Tuppence resorted to, Grant was thrilled.

Mrs. O`Rork Tuppence learns that Mrs. Sprot’s husband, the clerk, fearing the bombing, sent his wife and child to a boarding school and sometimes visits her. Mrs. Sprot whimpers all the time, worrying about her husband. Tuppence also learns that in the past Mrs. Perenna had some kind of drama, as she hides her origin. Sheila tells Tommy that her father participated in the Irish liberation movement, he was shot by the British, and now they are forced to hide. Mrs. Perenna falls under suspicion of the Birsford spouses.They do not take into account the rest of the women in the hostel, especially Mrs. Sprot, because the mother will not drag the child into espionage. But Mrs. O'Rourke is alarmed by Tuppence - she sees too much.

Near the guesthouse, Tuppence meets a poorly dressed woman of about forty. With a foreign accent, the stranger asks if a certain person lives in a guesthouse. Tuppence understands that the woman asked a question for averting her eyes, and she feels something suspicious in the stranger.

At the guesthouse, Tuppence accidentally overhears a telephone conversation between a man and a woman, which speaks of the fourth number.

Tommy visits Captain Haydock’s villa. During the conversation, the owner repeatedly repeats the story of how he caught a spy. Tommy compares this fact with the fact that just at that time, Mrs. Perenna bought her guesthouse, and his suspicions that she is a spy are growing stronger.

Having improved the moment when all the inhabitants of the boarding house are assembled, Tuppence reads aloud a letter allegedly from his son, in which he reports secret information. Soon, she again sees a mysterious stranger near the guesthouse, asking Karl about a certain Mrs. In the evening before going to bed, opening the drawer of the desk, Tuppence notices that someone read the letter from the “son”.

In the morning, little Betty rushes into Tuppence's room. The girl hands her an old tattered children's book, the first line of which is: "Geese, geese, where are you going?" Betty pulls the laces from Tuppence's shoes and puts them in a glass of water.

Putting a pungent powder under his bed, Tommy complains to Mrs. Perenna, and the hostess transfers him to another room, opposite the Tuppence room. Tommy starts to have a runny nose from the smell, and he spends all day in his room. Tuppence tells everyone that she received another letter from her “son” and is leaving on business. Tommy watches her room and sees that Carl has come in. She and Tuppence conclude that Mrs. Perenna, Sheila, Karl, and the stranger are spies. Having improved the moment, Tuppence sneaks into Mrs. Perenna’s room, but finds nothing significant. The hostess Tuppence, who entered the room, says that she is looking for a medicine, to which the hostess replies that Tuppence herself has this medicine, although she keeps this medicine in a closed drawer.

The stranger appears again near the guesthouse. In the evening, Mrs. Sprot notices that Betty has disappeared somewhere. The maid says she saw a stranger with Betty. Mrs. Sprot finds a note in her room threatening to kill her child if she calls the police. Captain Haydock provides his car and, together with Major Bletchley, Tommy, Tuppence and Mrs. Sprot, drives for the kidnapper. On the way, Mrs. Sprot shows Tuppence the little gun she took from the major.

They catch a fugitive on the top of the hill. The stranger approaches the cliff and with a hoarse howl presses the girl to herself. Haydock is afraid to shoot, but Mrs. Sprot calmly kills a woman, hitting her right on the forehead. Haydock is surprised by the accuracy of the shot.

Police establish that the stranger was a Polish immigrant Wanda Polonska, whose family was killed by the Germans. In England, the committee for assistance to immigrants found her a place for servants. According to witnesses, the woman showed signs of mental distress.

Tuppence wonders at Mrs. Sprot's behavior. First, she killed the kidnapper in cold blood, and now rolls up hysteria and is afraid to remember what happened. Tappence somehow comes to mind King Solomon, but she cannot understand why. A murdered woman vaguely reminds her of someone. The spouses' investigation comes to a standstill, but then the police arrest Karl as Wanda’s accomplice. During a search, he found laces soaked in a chemical - if they are immersed in water, chemical ink will be obtained. Tuppence suggests that Karl told Wanda to kidnap Betty, as the girl could have betrayed him.

Tommy and Tuppence call security officer Albert. Tommy is visiting captain Haydock.There he draws attention to his lackey Appledor, he seems Tommy suspicious. During the conversation, it comes to spies, and Tommy, for example, allegedly says: “N. or M. ". A footman breaks the dishes and sprinkles Tommy with liquor. Tommy goes to the bathroom and accidentally notices a radio transmitter there. The captain admits that he works in the special services, and asks Tommy to be silent. Tommy leaves, but near the guesthouse he is hit on the head.

Meanwhile, Tuppence is playing cards with Mrs. Cayley and Miss Minton. Mrs. Sprot, panting, enters the room, followed by Mrs. Perenna and Mrs. O'Rork with a hammer in her hand, which she found in the alley.

The next morning, the residents of the guesthouse are concerned about the absence of Tommy. Tuppence suspects that Mrs. O`Rork is involved.

The daughter of Tommy and Tuppence Deborah, who also works in the secret service, receives a letter from her mother, in which she informs that she is visiting with an elderly aunt. Since a friend of Deborah is traveling to those parts, the girl goes to visit her mother, but she does not find her at her aunt. Deborah finds out that her mother is in Scotland, in a guesthouse. Surprised, Deborah tells this to her colleague Tony. The next day, Deborah notices that a photograph of her mother disappeared from her room.

Tuppence meets Albert, who also knows nothing about Tommy. Albert reports that Mrs. Perenna, a member of the Irish Republican Army, is suspected of anti-English sentiment.

Tuppence is waiting for Tony at the guesthouse. He says the daughter is worried that the mother is here. Tony came to warn Tuppence about this. He says he knows what Deborah's parents do here. Tuppence tells Tony that Tommy is also here, and they have a nickname for the connection password.

Tommy wakes up in the basement, where Appledor brings him food. Captain Haydock is about to take the prisoner with the nearest boat. After they leave, Tommy suddenly hears singing, recognizes Albert's voice and snores the signals in Morse code.

Tuppence receives a postcard with the image of a Bonzo doggie and a letter signed by Tuppence. She cancels the tailor's fitting and announces that she is leaving for a few days. Mrs. Perenna shares her suspicions with Tuppence: Mr. Meadows is a spy, he talked with Carl for a long time. Before leaving, Tuppence notices that someone rummaged in her things. She heads to the train station, stepping on a road into a large puddle.

At the station, Tuppence meets Tony. He reports that Tommy is in captivity, and his captors are waiting for the boat. When the boat arrives, Tommy can be freed. Tony suggests that Tuppence impersonate a spy who, in the form of a sister of mercy, was parachuted and caught by the British secret services. Tuppence changes into a uniform, leaving her shoes, they make up and she goes to a meeting to be held by a dentist. There she meets Captain Haydock. Tuppence calls the date, the fourth, which causes the captain to be surprised. He knows that this is not a nurse, but Mrs. Blenkensop, who is actually Mrs. Birsford. The captain also knows that Mr. Meadows is her husband, Tommy. The captain threatens Tuppence, because in a make-up look no one will recognize her, and Tony works for them. In response, Tuppence says the first thing that comes to her mind, a line from Betty’s book: “Geese, geese, where are you going?” Haydock is furious. He leaves, leaving a woman in his place. The woman will not spare Tuppence, her son was killed in the last war, and she will avenge him. Her fierce expression resembles Tuppence Wanda, and she again recalls King Solomon.

Haydock is about to shoot at Tuppence as Grant bursts into the room and frees her. Tuppence rushes into a boarding house by car, finds a children's book about geese and gives it to Grant. She also introduces him to Mrs. M. — Mrs. Sprot.

Mr. Grant, Tommy, Tuppence and Albert discuss what happened. Hearing Tommy's snoring, Albert called Mr. Grant, and they grabbed the crew of the boat.Tuppence admits that she acted like the last fool, suspecting everyone, but not Mrs. Sprot. Communicating with Tony, she realized that he was a spy, because Tommy gave the task, and Tuppence was an unofficial person. She told the young man a false password - the real one was not her nickname, but a postcard with a Bonzo dog. Canceling the tailor's fitting meant that Tony had pecked. Albert poured some strong-smelling liquid near the guesthouse that Tuppence stepped into, and the dogs were able to trace her.

According to an accidentally thrown phrase about geese, Tuppence guessed that these words meant something to Haydock, and when she saw the expression on the face of the woman who was guarding her and Wanda, she remembered the parable about King Solomon and the two women who were arguing about whose child. Betty's mother was Wanda, an unhappy emigrant who gave the girl Mrs. Sprot, who was hiding behind a child. Mrs. Sprot wrote herself a note when Wanda abducted Betty. No wonder Wanda reminded someone of Tuppence. The children's books contained classified information, and Betty learned to lower the shoelaces into the water, of course, from Mrs. Sprot. Haydock called his accomplice, and Mrs. Sprott hit Tommy with a hammer on the head, and therefore came out of breath.

Sheila meets with Karl, an intelligence agent posing as Carl von Deining, his deceased friend. He suspected Tuppence of espionage and therefore climbed into her room.

Tommy and Tuppence decide to take little Betty to her upbringing.