The film follows notorious musician Serge Gainsbourg's exploits from his upbringing in German military administration in occupied France during World War II through his rise to fame and love affairs with Juliette Gréco, Brigitte Bardot and Jane Birkin to his later experimentation with reggae in Jamaica. It also incorporates multiple elements of fantasy, most significantly with the character called "The Mug", an animated exaggeration of Gainsbourg that acts as his conscience (or anti-conscience) at crucial moments in Gainsbourg's life. The film also includes many of Gainsbourg's more famous songs, which serve as the soundtrack to the film and often serve as plot elements themselves.