Michel Gauché (Jean-Paul Belmondo) is a professional film stuntman who works with his fiancée Jane Gardner (Raquel Welch). However minutes after their long planned marriage they are called to perform a car stunt for a movie but it goes wrong, as a brake problem causes their car to fall and they end up in a hospital with bruises and broken legs. Exasperated by the behavior of her fiancé, Jane decides to leave. After his recovery Michel is no longer able to find work in the movie business and is forced to simulate mental retardation and to invent a family to receive Social Security benefits. One day his stuntman friend Santos asks him to replace him from time to time at his job which involves dressing up as a gorilla for advertising pasta at a supermarket.
Michel's luck begins to improve as he gets offered a high salary to do the stunts of an effeminate movie star Bruno Ferrari (Jean-Paul Belmondo) whom he proves to be a dead ringer to. Ferrari while filming an action movie suffers from vertigo and finds himself unable to perform dangerous sequences. Michel does not hesitate to get rid of his new stunt partner in order to replace her with Jane, who is enamored with the Count of Saint-Prix (Raymond Gérôme). Having heard the news Michael goes to the Count while impersonating a server in order to propose the offer to Jane. When he hears that the Count has asked to marry Jane he manically sabotages the dinner and makes Jane promise to do the film.
Desperate to regain Jane, Michel impersonates Ferrari who turns out to be gay, to seduce her. However the young woman is not fooled. Michel must perform a dangerous stunt on the wing of an airplane to an audience of journalists who think they are seeing Ferrari, where his life is saved from the accident by Jane, who is to marry the Count very soon. Meanwhile, the press discovers that Ferrari is not doing his own stunts.
While the wedding ceremony takes place at the castle of the Count, Michel arrives disguised as a gorilla, scaring guests with animals from the property, and takes Jane, who refuses to marry Count of Saint-Prix, preferring to live her life with Michel.
Jean-Paul Belmondo as Mike / Bruno
Raquel Welch as Jane
Charles Gérard as Hyacinthe
Julien Guiomar as Fechner
Aldo Maccione as Sergio Campanese
Dany Saval as Doris
Raymond Gérôme as Count of Saint-Prix
Henri Génès : as Camille, café owner
Jane Birkin as The Female Star
Johnny Hallyday as The Male Star
Claude Chabrol as The Director
Mario David as Santos
Didier Flamand as The Cousin
Josiane Balasko as Supermarket Girl
Most of the stunts in the film were done by Belmondo himself. This caused him multiple injuries; a dislocated ankle after the scene on the steps of Sacré-Cœur, dislocation and a penetrating wound after the scene in which he is tumbling down the stairs, a chewed up ear after the fight scene with a tiger. Because the insurance companies refused to insure aerial stunts they had to be filmed last. Everything went off without incident, and the actor was able to realize his childhood dream of personally standing on the wing of a flying airplane.