Meursault is a shipping clerk living in a decrepit Algiers apartment he shared with his mother before he sent her to an old people's home he rarely visits. The novel opens when he receives a telegram saying his mother has died. Meurseult isn't upset. Meursault meets with the director of the home who quells Meursault's inner defensiveness about sending his mother away by assuring him she was happier at the home than she would have been in Algiers. He tells Meursault he's arranged a religious funeral, in accordance with her wishes, though Meursault reflects privately that his mother wasn't religious. Meursault goes to the mortuary and surprises the caretaker by declining to see his mother's body. They drink coffee and smoke together, then sit vigil over the coffin with his mother's friends, whose crying irritates the unemotional Meursault. Next morning, the funeral procession is joined by Thomas Pérez, Mme. Meursault's closest friend (and rumored fiancé). They walk across the hot, shimmering landscape to church for the funeral, which Meursault barely remembers.
Saturday, Meursault goes to the beach and runs into Marie. They swim, flirt, go to a comedy, and go home together. Marie is startled to hear Meursault's mother just died. Monday, Meursault's neighbor Raymond invites him to dinner and recounts his thirst for revenge on his mistress. He gets Meursault to write a letter luring her back to shame her. Pleased, Raymond now considers Meursault his friend.
Next Saturday, Meursault and Marie hear Raymond beating his mistress. A policeman frees her, shaming Raymond. Later, Meursault agrees to Raymond's request that he testify to her infidelity. He meets Salamano who is heartbroken after losing the dog he's always pretended to hate.
At work, Meursault declines a transfer to Paris since "nothing mattered." When Marie asks if he wants to marry her, he says it makes no difference but he will if she wants.
Sunday, Marie, Meursault, and Raymond go to Masson's bungalow. Raymond worries he's being followed by the Arab, his mistress' brother. At the beach, Meursault and Marie are happy. Meursault, Masson, and Raymond walk on the beach, running into the Arab and his friend. Raymond starts a fight but surrenders when cut by the Arab. Furious, Raymond insists on returning to the beach. Meursault follows. They meet the Arabs but Meursault has Raymond give him his gun. The Arabs retreat. Dizzy with heat, Meursault wanders alone along the "dazzling, red glare." He is "surprised" to meet the Arab again, who draws his knife. At the "dazzling spear" of sun reflecting off it, Meursault shoots the man.
In prison, the examining magistrate attempts unsuccessfully to Christianize Meursault. Marie visits once, but is barred from visiting again. Meursault acclimates to prison and spends his days remembering his apartment. A year passes.
The trial is blown up by the press and the courtroom is packed. Much is made of Meursault's insensitivity at his mother's funeral and the director and caretaker testify to Meursault's coldness. After Meursault's lawyer makes progress, Marie inadvertently cripples the defense by recounting her first date with Meursault the day after his mother's funeral. Meursault's lawyer attempts to rescue the case – "is my client on trial for burying his mother or for killing a man?" – but the prosecutor connects the funeral and the murder, portraying Meursault as a soulless monster premeditating murder at his mother's grave. Throughout the trial, Meursault is mostly calm, only rankling when he feels excluded from the proceedings. In closing remarks, the prosecutor equates Meursault's crime with the parricide being tried in court next day, claiming Meursault is "morally guilty of killing his mother." Meursault is sentenced to death.
Meursault files for appeal. Obsessed by the arbitrariness of his verdict and the certainty of death by guillotine, he fantasizes a justice system that would give the condemned "a chance." He tries to be levelheaded, imagining both possible outcomes of his appeal, but feels "delirious joy" whenever he thinks of living. The chaplain visits and lectures Meursault on the afterlife. Meursault screams that there's no existence but this one, that all people are equally privileged and condemned. He feels "rid" of "hope" and is "happy." He "opens…to the gentle indifference of the world," and thinks he need only be accompanied by "cries of hate" "to feel less alone."