The Stranger is a description of the last days of the narrator, a man named Mersault. Mersault is the mature Holden Caulfield. He goes through his life with little thought of others; primarily because he gives little thought to himself. He just goes about and lets the events of life bounce off him, indifferent to any aspirations for himself, puzzled by aspirations in other people. When his mistress asks if he loves her: “I answered . . . that it didn't mean anything, but that I probably didn't love her.” When his mother dies, he obliges the social conventions–to sit at casket vigil for a day–but feels no remorse; he doesn't feel any annoyance at the vigil, either; he simply doesn't care either way.
It's this indifference, this superhuman detachment, that gets Mersault sentenced to death. He becomes friends with a pimp named Raymond, who at one point beats his girlfriend, an Arab woman. The woman's brothers later attack Raymond in revenge while Mersault is with him. The Arabs are beaten back. Later, they see the Arabs again, and Raymond proposes to shoot them in cold blood. Mersault advises against it and convinces Raymond to give the revolver to him. Later Mersault is walking alone on the beach and, on the verge of heat stroke, sees one of the Arabs again. In order to get out of the sun, he walks towards the shade, which is in the Arab's direction; the Arab pulls a knife, and Mersault, in self-defense, shoots him–five times.
At his subsequent trial, Mersault is convicted of murder. One of the primary pieces of evidence: His callousness at his mother's funeral. He must, the prosecutor convinces the jury, be a monster. He is sentenced to death. While awaiting his execution, the prison chaplain visits him and urges him to reconcile himself with Christ. Mersault, naturally, is indifferent to anything like religion or the after-life and doesn't see any sense in the chaplain's urgings, which don't relent until Mersault blows up at him, crying out that none of it makes any difference; all men are equally worthy; all men live under a sentence of death. It doesn't matter that his mother died; it doesn't matter if his girlfriend is now kissing another man. It all doesn't matter.
In short, no matter what, the universe stands silent. So how can all these things–these things that seem to matter to people–matter? Prior to this emotional explosion, Mersault was disturbed at his pending death. After it, he was calm and welcomed it. Camus made it clear that Mersault, always the stranger, had finally become conscious of the absurdity of life, of why he was a stranger and properly so, and could now greet death with indifference, too.