All the action of Mrs. Dalloway takes place in London during one day and night in mid-June, 1923. Clarissa Dalloway is an upper-class housewife married to Richard, a politician in the Conservative Party. Clarissa is throwing a party that night, and in the morning she walks about London on her way to get flowers. She enjoys the small sensations of daily life and often muses on her late teenage years at Bourton, her family’s country home. She passes a car bearing an unknown but important personage, and an airplane sky writing an advertisement.
Clarissa returns home and is visited by Peter Walsh, an old friend from Bourton who has been in India for years. Peter was once passionately in love with Clarissa, but she rejected his offer of marriage. Peter and Clarissa have always been very close but also very critical of each other, and their brief meeting is laden with shared memories. Peter leaves when Clarissa’s daughter Elizabeth enters, and he walks to Regent’s Park, thinking about Clarissa’s refusal of his marriage offer. He follows a young woman, idealizing her from afar.
The point of view shifts to Septimus Warren Smith, a veteran of World War I who is suffering from shell shock. Septimus and his Italian wife, Lucrezia, wait in Regent’s Park. Septimus imagines that he is a kind of prophet and has hallucinations of his dead soldier friend Evans. Septimus was once an aspiring poet, but after the war he became numb and unable to feel. He believes his lack of emotion is a crime for which the world has condemned him to death, and he is often suicidal. Lucrezia has been taking Septimus to Dr. Holmes, who is convinced that Septimus has nothing wrong with him and is “in a funk.” That afternoon the Smiths visit Sir William Bradshaw, a famous doctor who subscribes to a worldview of “proportion” and is a psychological bully to his patients. Sir William plans to send Septimus to a mental institution in the country.
Richard Dalloway has lunch with Lady Bruton, a descendant of famous generals, and Hugh Whitbread, a shallow but charming aristocrat. The men help Lady Burton write a letter about emigration. After lunch Richard gets roses for Clarissa and plans to tell her he loves her, but when he sees her finds he cannot say it out loud. Clarissa considers the privacy of the soul and the gulf that exists between even a husband and a wife. Richard leaves and Elizabeth emerges with Doris Kilman, her history tutor. Doris Kilman is poor, unattractive, and bitter, and has been trying to convert Elizabeth to Christianity. Miss Kilman and Clarissa hate each other and are jealous of the other’s influence on Elizabeth. Miss Kilman and Elizabeth go shopping and then Elizabeth leaves, leaving Miss Kilman to wallow in hatred and self-pity.
Septimus grows suddenly lucid while Lucrezia is making a hat. The couple designs the hat and jokes together, sharing a moment of happiness. Then Dr. Holmes arrives to visit Septimus. Lucrezia tries to stop him, but Holmes pushes past her. Septimus thinks of Holmes as a monster condemning him to death, and Septimus jumps out the window, killing himself as an act of defiance.
Peter hears the ambulance go by and marvels at it as a symbol of English civilization. He lingers at his hotel and then goes to Clarissa’s party, where most of the novel’s upper-class characters eventually assemble. Clarissa acts as a “perfect hostess” but is worried the party will fail, and she is aware of Peter’s silent criticism. Sally Seton, a woman Clarissa had loved passionately as a teen at Bourton, arrives unexpectedly. The once-radical Sally has married a rich man and settled down. The Prime Minister visits briefly but his appearance is anticlimactic. Sir William Bradshaw arrives late, and his wife tells Clarissa about Septimus’s suicide. Clarissa goes off alone to consider the sudden arrival of death at her party, and she feels a kinship with Septimus. She admires the purity of his soul and considers her own often shallow existence. She sees Septimus’s suicide as an act of communication. Peter and Sally reminisce, waiting for Clarissa to join them. Clarissa finally appears and Peter is filled with ecstasy and terror.