The novel has two main narrative lines involving two separate characters (Clarissa Dalloway and Septimus Smith); within each narrative there is a particular time and place in the past that the main characters keep returning to in their minds. For Clarissa, the "continuous present" (Gertrude Stein's phrase) of her charmed youth at Bourton keeps intruding into her thoughts on this day in London. For Septimus, the "continuous present" of his time as a soldier during the "Great War" keeps intruding, especially in the form of Evans, his fallen comrade.
Septimus, as the shell-shocked war hero, operates as a pointed criticism of the treatment of mental illness and depression. Woolf criticises medical discourse through Septimus' decline and suicide; his doctors make snap judgments about his condition, talk to him mainly through his wife, and dismiss his urgent confessions before he can make them. Rezia remarks that Septimus "was not ill. Dr Holmes said there was nothing the matter with him."
Woolf goes beyond commenting on the treatment of mental illness. Using the characters of Clarissa and Rezia, she makes the argument that people can only interpret Septimus' shell shock according to their cultural norms. Throughout the course of the novel Clarissa does not meet Septimus. Clarissa's reality is vastly different from that of Septimus; his presence in London is unknown to Clarissa until his death becomes the subject of idle chatter at her party. By never having these characters meet, Woolf is suggesting that mental illness can be contained to the individuals who suffer from it without others, who remain unaffected, ever having to witness it. This allows Woolf to weave her criticism of the treatment of the mentally ill with her larger argument, which is the criticism of society's class structure. Her use of Septimus as the stereotypically traumatised veteran is her way of showing that there were still reminders of the First World War in London in 1923. These ripples affect Mrs. Dalloway and readers spanning generations. Shell shock, or post traumatic stress disorder, is an important addition to the early 20th century canon of post-war British literature.
There are similarities in Septimus' condition to Woolf's struggles with bipolar disorder. Both hallucinate that birds sing in Greek, and Woolf once attempted to throw herself out of a window as Septimus does. Woolf had also been treated for her condition at various asylums, from which her antipathy towards doctors developed. Woolf committed suicide by drowning, sixteen years after the publication of Mrs Dalloway.
Woolf's original plan for her novel called for Clarissa to kill herself during her party. In this original version, Septimus (whom Woolf called Mrs. Dalloway's "double") did not appear at all.
When Peter Walsh sees a girl in the street and stalks her for half an hour, he notes that his relationship to the girl was "made up, as one makes up the better part of life." By focusing on characters' thoughts and perceptions, Woolf emphasises the significance of private thoughts rather than concrete events in a person's life. Most of the plot in Mrs Dalloway consists of realisations that the characters subjectively make.
Fueled by her bout of ill health, Clarissa Dalloway is emphasised as a woman who appreciates life. Her love of party-throwing comes from a desire to bring people together and create happy moments. Her charm, according to Peter Walsh who loves her, is a sense of joie de vivre, always summarised by the sentence: "There she was." She interprets Septimus Smith's death as an act of embracing life and her mood remains light, even though she hears about it in the midst of the party.
As a commentary on inter-war society, Clarissa's character highlights the role of women as the proverbial "Angel in the House" and embodies sexual and economic repression and the narcissism of bourgeois women who have never known the hunger and insecurity of working women. She keeps up with and even embraces the social expectations of the wife of a patrician politician, but she is still able to express herself and find distinction in the parties she throws.
Her old friend Sally Seton, whom Clarissa admires dearly, is remembered as a great independent woman: She smoked cigars, once ran down a corridor naked to fetch her sponge-bag, and made bold, unladylike statements to get a reaction from people. When Clarissa meets her in the present day, Sally turns out to be a perfect housewife, having married a self-made rich man and given birth to five sons.
Clarissa Dalloway is strongly attracted to Sally Seton at Bourton. Thirty four years later, Clarissa still considers the kiss they shared to be the happiest moment of her life. She feels about Sally "as men feel," but she does not recognise these feelings as signs of homosexuality.
Similarly, Septimus is haunted by the image of his dear friend Evans. Evans, his commanding officer, is described as being "undemonstrative in the company of women." The narrator describes Septimus and Evans behaving together like "two dogs playing on a hearth-rug" who, inseparable, "had to be together, share with each other, fight with each other, quarrel with each other...." Jean E. Kennard notes that the word "share" could easily be read in a Forsteran manner, perhaps as in Forster's Maurice, which shows the word's use in this period to describe homosexual relations. Kennard is one to note Septimus' "increasing revulsion at the idea of heterosexual sex," abstaining from sex with Rezia and feeling that "the business of copulation was filth to him before the end."