Based on a story by Graham Greene, a boy without his parents likes the butler but learns he has a secret friendship with a woman which he must tell about after the butler's wife dies.
The boy Phillipe (Bobby Henrey) is alone in the embassy with the butler Baines (Ralph Richardson), whom he likes, and Mrs. Baines (Sonia Dresdel), who scolds him not to lie. Phillipe has a pet snake but keeps it secret from Mrs. Baines. Phillipe runs after Baines and sees him with Julie (Michele Morgan) in a café. She is sad and leaves, but in the street Baines promises to talk to his wife. Baines warns Phillipe not to tell Mrs. Baines about Julie.
Phillipe watches Baines tells his wife that he wants his freedom. Mrs. Baines sees milk on Phillipe's clothes and learns where he was. She pretends to go away but stays and hides. Baines wakes up Phillipe, and they go out. Baines tells Phillipe how he killed an African in self-defense. They meet Julie, and Baines says he has not yet told his wife about her. Julie says the boat-train is at nine. They go to a zoo. Baines reads a telegram from Mrs. Baines and says she will not be back for a day or two. Phillipe's snake is gone, and Baines consoles him.
In the evening they play hide and seek. Phillipe goes to bed, and Mrs. Baines comes to him. She struggles with Baines, and he walks away. Mrs. Baines falls from a ledge to the bottom of the stairs. Phillipe sees this and runs in the street. A policeman takes him to the station. The suicide is reported, and they take Phillipe home.
Baines says she slipped. Dr. Fenton (Walter Fitzgerald) questions Phillipe, who says that Mrs. Baines was angry because of secrets. Dr. Fenton asks for a police doctor. Baines tells Phillipe to forget what he saw. Phillipe finds the telegram he made into a glider. Detective Ames (Jack Hawkins) picks it up and questions Baines.
Julie arrives early in the morning, and Baines says she works in the typing pool. Inspector Crowe (Denis O'Dea) questions Baines and Julie, who urges Phillipe to tell the truth. Julie admits she was there. Baines says that Mrs. Baines was hitting Phillipe. He describes where they struggled but denies he pushed her down the stairs. Phillipe says that Baines did not murder her and says that Mrs. Baines hit him. Baines tells Phillipe that he lied about Africa. Police find evidence on the ledge. Phillipe asks them to listen to him, but they ignore him. Finally he says that he upset the flowerpot, and they have cleared Baines. Phillipe's mother comes home, and he greets her happily.
The audience sees this mystery unfold from the viewpoint
of a child, who learns that adults have confusing standards about
lying and not lying. After they find out he has lied, they no
longer believe him anymore even though he is the only one who
saw what happened.