The action takes place at the beginning of the 19th Century in Southern Sweden, in the Egerman household, the local theatre and lodgings of Desiree Armfeldt, an actress, and at the Ryarp manor house owned by her mother.

Anne Egerman, the frigid, virginal, young wife of middle-aged lawyer Fredrik Egerman, rebuffs the physical advances of her husband. Fredrik goes to visit his former mistress, Desiree Armfeldt, falls in a puddle of water and, while his clothes are drying, borrows a nightshirt and cap belonging to her current lover, Count Malcolm. A young child appears and to his astonishment, Fredrik learns he is the boy's father. Count Malcolm makes a stormy entrance with jealous accusations and counter accusations being made.

Next day, Desiree persuades her mother to throw a party on her Estate. The Malcolms and the Egermans are invited including Fredrik's adult son Henrik who is a theology student. Count Malcolm has hinted to his wife, Charlotte, that Fredrik is an "intimate" friend of Desiree. Charlotte conveys this to Anne, who proudly declares she is aware of the liaison. A maid Petra attempts to seduce Henrik but he wards off her advances quoting the scriptures. Anne and Henrik are attracted to each other.

At dinner on the Ryarp Estate, Old Mrs Arnfeldt slips a love potion into the food. Fredrik becomes aware of the attraction Anne feels for his son and Charlotte, having made a bet with her husband, attempts to seduce Henrik. Upset by the cynical conversation at the table Henrik leaves and tries to commit suicide. Planning to hang himself from a damper, he accidentally touches an alarm on the wall. Bells ring and the bed in an adjoining room comes rolling into his room with the sleeping Anne in it. Later that night the two run off together with the assistance of Petra, while Fredrik, unknown to them, is watching from a distance.

To defend his honour, Count Malcolm has challenged Fredrik to a game of Russian roulette in a pavilion in the grounds of the Estate. Fredrik ends up being the loser in this lethal game and, having shot the pistol, stumbles out with a black face, the pistol having been loaded only with soot. Charlotte is reconciled with her husband and Fredrik, sad and lonely, returns to Desiree, which was Desiree and her mother's plan all along.

The sun rises over the summer night and Petra and Frid, the groom, are seen rolling in the hay.