La Nuit américaine chronicles the production of Je Vous Présente Paméla (Meet Pamela), a clichéd melodrama starring aging screen icon, Alexandre (Jean-Pierre Aumont), former diva Séverine (Valentina Cortese), young heart-throb Alphonse (Jean-Pierre Léaud) and a British actress, Julie Baker (Jacqueline Bisset) who is recovering from both a nervous breakdown and the controversy leading to her marriage with her much older doctor. In between are several small vignettes chronicling the stories of the crew-members and the director; Ferrand (Truffaut himself) tangles with the practical problems one deals with when making a movie. Behind the camera, the actors and crew go through several romances, affairs, break-ups, and sorrows. The production is especially shaken up when Alphonse's fiancee leaves him for the film's stuntman, which leads him to a one night stand with Julie, when one of the secondary actresses is revealed to be pregnant, and when Alexandre is killed suddenly in a car crash.
Source : Wikipedia