In this autobiographical novel, Plath's protagonist, Esther Greenwood, sinks into a profound depression during the summer after her third year of college. Esther spends the month of June interning at a ladies' fashion magazine in Manhattan, but despite her initial expectations, is uninterested in the work and increasingly unsure of her own prospects.

Esther grows disenchanted with her traditional-minded boyfriend, Buddy Willard, a medical student who “had won a prize for persuading the most relatives of dead people to have their dead ones cut up, whether they needed it or not . . . . ” Returning home to a New England suburb, Esther also discovers that she's been rejected from a Harvard summer school fiction course. Her relationship with her mother is painfully strained.

Suddenly, Esther finds herself unable to sleep or read or concentrate. She undergoes a few unsuccessful sessions with a psychiatrist, Dr. Gordon, as well as terrifying electroshock therapy. She becomes increasingly depressed, thinks obsessively about suicide, then attempts to kill herself by crawling into the cellar and taking a bottle of sleeping pills: "red and blue lights began to flash before my eyes. The bottle slid from my fingers and I lay down." Esther vomits, however, and so, does not die. She is taken to a city hospital and then, through the financial intervention of a benefactor, to a private psychiatric institution.

There, Esther begins gradually to recover. She enjoys the pleasant country-club surroundings and develops a closeness with her analytically-oriented psychiatrist, Dr. Nolan. Esther also undergoes a more successful regimen of shock therapy, after which she feels the "bell jar" of depression lifting.

The stigma of attempted suicide and hospitalization seems to free Esther to behave less traditionally; defiantly, she loses her virginity to a man she's met on the steps of Harvard's Widener Library. At the novel's end, Esther is preparing to leave the psychiatric hospital and is describing herself, optimistically, as transformed.