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.

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.

Recovering from an attempted suicide, a man is selected to participate in a time travel experiment that has only been tested on mice. A malfunction causes the man to experience moments from his past in a random order.

In late 19th century France, the Countess Louise, wife of a wealthy general, sells the earrings her husband gave her on their wedding day to pay off her secret debts, then claims to have lost them. Her husband quickly learns of the deceit, which is the beginning of many tragic misunderstandings, all involving the earrings, the general, the countess, and her new lover, the Italian Baron Donati.

Diego is one of the chiefs of the Spanish Communist Party. On his way from Madrid to Paris, he is arrested at the border for an ID check but manages to get free. When he arrives in Paris, he starts searching for one of his comrades to prevent him from going to Madrid where he could be arrested.