Five men pretending to be musicians practicing plan a robbery and use an old lady as an unwitting accomplice. Just as they are about to get away with the money, things start going wrong.
Mrs. Wilberforce (Katie Johnson) comes to the police station, and the Superintendent is glad to see her. She opens her umbrella in the rain and goes home. She hammers a pipe to get the water running. A man rings at the door, and Professor Marcus (Alec Guinness) comes in to rent a room. She has been alone there, and he takes the room. He asks if he and his musician friends could practice there, and she agrees. She has parrots. He says he likes the windows.
The next day he answers the door, and his friend Claude or Major Courtney (Cecil Parker) comes in, followed by One Round or Mr. Lawson (Danny Green) and by Harry or Mr. Robinson (Peter Sellers). She welcomes them, and they go upstairs. She answers the door, and Louis or Mr. Harvey (Herbert Lom) comes in. She says she is happy they are all there.
Marcus puts on a record of a quintet, and they start talking about their plan. They discuss the old lady. When they hear a knock, they pick up their instruments. She brings in a tray and praises their musical skill. Louis says he wants the old lady out, and Marcus puts it to a vote. One Round is the deciding vote to accept her, and Louis decides to stay.
Marcus films the unloading of a truck. When the old lady comes to the door, Claude says they do not want any tea. She asks for help with her parrot, and Harry volunteers. Harry screams after being bitten by the bird which gets out of its cage. One Round stands on a chair and breaks the chair. Louis breaks the record. The parrot flies out the window. She says she phoned the police. Claude and Louis go on the roof. On the street Marcus picks up the parrot and gives it to the lady.
The five men wait in a car. Three get out. One goes in a truck, one in a car, and the other walks. They block a truck, and then wearing scarves over their faces, they remove the two men and pry open the back of the truck. They break into the back and unload metal boxes into their black car. A policeman runs after their white car. Harry moves three trunks on a dolly and puts them on a baggage train. Police report an armed robbery but say there is no trace of stolen property. The old lady arrives, and Harry sees her. She goes to collect a trunk for Marcus. He goes into a phone booth, looks at a watch, and answers it. He tells Claude to listen as he says she is driving away. Claude says she came back, and Marcus gets upset. Louis comes into the phone booth with Marcus. She says she forgot her umbrella. The five men get in the black car. They see her on the street talking to the Barrow Boy (Frankie Howard) with a horse pulling a cart of fruit. She insists a man do something to stop his brutality. She hits the Barrow Boy with her umbrella, and a fight starts. Marcus says to drive around the block and come back. A policeman tries to settle the squabble. They come back and see the trunk on the street. The lady talks with the police in the station.
The five men come in the house and see the large trunk. They happily carry it upstairs and open four metal boxes of money. They all leave with their metal boxes. One Round says goodbye, but part of his cello case is stuck in the door. He rings, and she opens the door. The case comes open, and money scatters. They all pick up the money and drive off. Louis says they must go back, or else she may report them. They all go back and try to explain about the money she saw. Louis says they must get her out of there. Other old ladies come to the door, and she lets them in. One looks at a newspaper and tells them about a robbery of £60,000. Harry goes out to move the car. Mrs. Wilberforce tells Marcus that she is shocked. She says they must come in among her oldest friends for one hour. Harry returns and joins them. They drink tea and sing as Marcus plays piano.
Later the ladies leave. Marcus tells her that nobody wants the money back because it was insured. Marcus says they are all burdened with responsibilities. Claude says he is caring for an invalid. Marcus says he planned the robbery to help them. She doubts the justification. Marcus informs her that the police are after her too. Marcus says they will protect her. Louis says he will say she planned the job. A policeman comes to the door, and Marcus instructs her not to let him in without a search warrant. The sergeant (Philip Stainton) tells her they won’t be needing her at the station. She asks if he has a search warrant. He knocks again and asks if she is all right. Marcus tells her not to talk to the police. She says she must go to the police and give herself up.
Upstairs they discuss how to kill her. Marcus says it must look like an accident. They cannot decide who is to do it. She comes in and says they must go the police, but they persuade her to postpone it because of the rain. Louis pulls out a knife and cuts matches for a drawing. They each draw a match, and Claude gets the short stick. At first he refuses and then he says he will do it. He asks them to send her up there. Marcus asks her to go up to speak to him privately. She comes in. The other four wait downstairs. Claude says they will not let her go to the police. He admits they are criminals. He says he will go to the police, and he goes out the window. One Round opens the back door. The others discover her and that Claude is gone. They start looking for him, and Marcus sees him on the roof. Three climb up, and Louis falls down. The cello case falls off the roof, and Harry catches it. Claude and Louis are sitting on a pipe. Louis forces him off and says he did not feel a thing.
One Round says he changed his mind and will not do it, and he will not let anyone else touch her. Marcus tells One Round that he must get rid of Claude’s body. The other three draw, and Harry gets the short stick. Marcus goes with One Round who takes the body in a wheel barrow. Harry has a gun and puts it in his coat. He prepares to use his tie and goes in. She is sitting asleep, and he takes a key. One Round and Marcus drop the body into a coal car. Marcus sends One Round to fetch the car. One Round runs in and thinks she is dead. He runs after Harry, who goes in a building. One Round breaks down the door and runs after Harry. She wakes up, and One Round comes back angry. She says someone took the key, and she is angry. She takes the cello case. One Round refuses to put Harry in the barrow. He goes in to stay with her.
Louis and Marcus drop the body of Harry onto a train. They talk about who will kill One Round and the lady. One Round holds a gun on them but cannot shoot. Louis says the catch was on. Marcus says his plan needed more men to kill her. Louis shoots at hiding Marcus. Louis climbs over the wall, and Marcus gets his gun. He pushes him into the coal train. A beam comes down and knocks Marcus out and into a train car.
Mrs. Wilberforce tries to talk to the police and says they all disappeared during the night. She says she has all the money. They do not believe her and tell her to forget it and not mention it. They say she can just keep the money. She says they do not want the money back. The policeman says she forgot her umbrella, but she says she can buy a dozen new ones. She gives some money to a beggar.
This droll comedy mixes a genteel situation with a major robbery and murder, making the contrast seem ludicrous. The poetic justice and irony are that all the criminals eliminate each other while their innocent target remains untouched and gets away with the money.