Claude Massoulier is murdered while hunting at the same place as Julien Vercel, an estate agent who knew him and whose fingerprints are found on Massoulier's car. As the police discover that Marie-Christine Vercel, Julien's wife, was Massoulier's mistress, Julien is the prime suspect. But his secretary, Barbara Becker, while not quite convinced he is innocent, defends him and leads her private investigations.
The third in a series of films featuring François Truffaut's alter-ego, Antoine Doinel, the story resumes with Antoine being discharged from military service. His sweetheart Christine's father lands Antoine a job as a security guard, which he promptly loses. Stumbling into a position assisting a private detective, Antoine falls for his employers' seductive wife, Fabienne, and finds that he must choose between the older woman and Christine.
Parisian everyman Antoine Doinel has married his sweetheart Christine Darbon, and the newlyweds have set up a cozy domestic life of selling flowers and giving violin lessons while Antoine fitfully works on his long-gestating novel. As Christine becomes pregnant with the couple's first child, Antoine finds himself enraptured with a young Japanese beauty. The complications change the course of their relationship forever.
