"Maman died today." This is the first line of Albert Camus' great existential novel, The Stranger. The narrator and protagonist, Meursault, receives a telegram telling him that his mother has died in her retirement home. He isn't sure when she died, exactly, and his apparent indifference to the fact of her death puts people off. He takes the bus to Marengo, where she died, to sit vigil. Her friends from the home also attend, and their displays of grief make Meursault uncomfortable. His mother's fiancé, Thomas Peréz, joins the funeral procession, heartbroken over his loss. Meursault doesn't cry.
On the Saturday after the funeral, he decides to go to the beach. There, he meets Marie, a former coworker. He sleeps with her, then returns home. His apartment is too big for him, and ever since his mother moved into the home he has been living in a single room, having no need of the extra space. He sits in his room, staring out at the people on the street. When night falls, he gets up and thinks that, despite Maman's death, nothing has changed.
Meursault returns to work on Monday. His boss is nice to him, and he works hard. His coworker, Emmanuel, joins him for lunch at the usual place, Céleste's. That night, Meursault speaks to two of his neighbors, one of whom (Salamano) has a dog with a skin condition. His other neighbor, a man named Raymond, recently got into a fight with the brother of his Arab mistress, whom he'd been "keeping," as in paying her way. (In the French, Camus uses the term "Arabe," a pejorative word often used by French colonists.) Raymond found out she was cheating on him and beat her up. Now he wants to punish her, so he asks Meursault to write her a nasty letter.
Marie spends the night on Saturday. The next morning, they overhear a fight between Raymond and his mistress. One of their neighbors calls the cops, and Raymond is told to await a call from the police precinct. That afternoon, he visits Meursault. Meursault agrees to testify at Raymond's trial. Together, they go for a walk, then shoot some pool. When they return, Salamano tells them he lost his dog.
Meursault is at work when Raymond calls to invite him to a friend's beach house near Algiers for the weekend. Raymond also says that a small group of Arab men, including his mistress' brother, has been following him. Meursault's boss offers him a promotion, but Meursault doesn't care one way or the other. Nor does he care if he marries Marie or not. She thinks he's peculiar, but doesn't break up with him. He eats dinner alone at Céleste's, where a woman sits at his table, but doesn't speak. He goes home to find his neighbor Salamano upset. Evidently, the dog has disappeared.
Meursault, Marie, and Raymond head to the beach house, where they meet Masson and his wife. It's a hot, sunny day, and Meursault dislikes being in the sun when he's not swimming. After they eat, the three men go for a walk on the beach, where they're attacked by two Arabs, one of whom has a knife. Raymond is injured, but patched up. Later, Raymond and Meursault go for a walk on the beach, where they see the Arabs again. Raymond has his gun with him, but Meursault takes it away. Later, Meursault shoots one of the men.
Meursault speaks to a magistrate after being arrested. He has been appointed an attorney, but isn't much interested in his trial or defense. Both his lawyer and the magistrate take offense at the fact that Meursault shows no emotion, either about his crime or his mother's death. His "insensitivity" hurts his case. The magistrate begins calling Meursault "Monsieur Antichrist."
In prison, Meursault lives briefly with some Arab cellmates before receiving a cell of his own. It doesn't take long for Meursault to feel at home there. Marie visits him, trying to reassure him that he'll be acquitted. She's forced to shout, because the visiting room is very crowded, and the noise make Meursault ill. After this visit, Meursault begins to feel closed in by his cell; but that passes. He realizes that his mother was right: given enough time, you can get used to anything.
Meursault loses track of time in prison and begins talking to himself. He finds an old newspaper clipping about a Czech man who was killed by his mother and sister, who hadn't recognized him after his long absence. While Meursault is awaiting trial, the press gets hold of his story and runs with it. When he arrives in court, there's a large crowd. After the jury is selected, the judge starts to question him. This doesn't go well for Meursault.
Following Meursault's questioning, a series of witnesses are called to testify against his character in court. When the caretaker says that Meursault drank a cup of coffee and smoked a cigarette at his mother's funeral, the prosecutor argues that Meursault is a monster because of it. Then Marie takes the stand, and the courtroom falls silent when they hear that she and Meursault went to see a movie (a comedy) on the day after Maman's funeral. Raymond's testimony reflects poorly on Meursault, because Raymond is a pimp and therefore a known degenerate.
Meursault finds the prosecutor's summation boring. He knows that the prosecutor is twisting the facts to paint an overly negative picture of things. Meursault finallys says that he killed the man "because of the sun." His lawyer makes an impassioned speech on his behalf, to no avail. After a short recess, the jury returns with a guilty verdict. Meursault is sentenced to death by guillotine.
While awaiting execution, Meursault's thoughts are consumed by his appeal. He knows it will be denied, but this doesn't keep him from imagining it on a daily basis. He refuses to see a chaplain, thinking instead of his impending death and of what it will feel like to die. The chaplain comes to visit against Meursault's wishes, but grows frustrated when Meursault insists that there's no hope and that he will never turn to God. Finally, Meursault snaps and makes the chaplain cry with his shouts of rage, portending his existential doom. When the chaplain leaves, Meursault accepts his fate happily.