During a scandalous broken engagement, Miss Julie, the daughter of Count Carl, forgoes a family Midsummer's Eve celebration to attend the estate servants' ball, choosing to mingle with people who normally stand at the bottom of the social ladder. There, she dances with one of the servants, Jean, whom she finds herself increasingly drawn to. She orders him to sit at the table with her for beers and humiliates him by making him kiss her shoe. Outside, she makes advances on him; the hand, hidden behind a sculpture, witnesses the encounter in shock. Miss Julie asks Jean if he has ever been in love. He replies that he loved her as a boy when he lived in poverty and saw her on the estate, but he was chased off as an "urchin." The servants march forward, singing and looking for Jean; Julie and Jean realize the scandal that will erupt if they are seen together and attempt to escape and hide, but the hand has already told of what he saw.
Jean and Julie contemplate escape; Jean condemns the tradition and class bias of Sweden, expressing a desire to take a train to Italy, where he could run a hotel with investment capital from Julie. Julie counters that she has no money of her own and is shocked by his sudden demeanor of callousness toward her. He is unconcerned about her fears of the Count learning of the scandal and reveals he is not willing to die for her, as he had suggested. He then recounts his boyhood, and Julie retells her own girlhood: her mother, Countess Berta, a commoner who believed in women’s rights, had to be persuaded to marry; Julie was dressed in boys’ clothes, but she preferred playing with dolls. The Countess set fire to their home, and the Count later attempted suicide by firearm. Upon hearing the story, Jean declares himself of superior heritage, as Julie is the daughter of an arsonist.
Before leaving on Midsummer's Day, Jean sees Julie's finch Serine and declares they cannot take a birdcage. When Julie says she would rather Serine die than be left behind, Jean breaks its neck; Julie curses him and the day she was born. When the Count returns, he finds Julie has killed herself by razor, beneath the portrait of the Countess.