An unnamed narrator, who promises to reveal his identity later, states that the chronicle that follows is as objective as possible. He assures the reader that he reports only those things he witnessed himself, the eyewitness accounts he received first hand, and a written eyewitness account of the events in question.
In the Algerian city of Oran, Dr. Bernard Rieux steps out of surgery and finds a dead rat lying on the landing. In the days that follow, an increasing number of rodents stagger out into the open and die, blood spurting from their muzzles. Dr. Rieux, preoccupied by his wife's impending trip to a sanitarium, doesn't give a great deal of attention to the phenomenon at first. M. Michel, the concierge for the building where Dr. Rieux works, is convinced that the dead rats in the building have been placed there by pranksters. Dr. Rieux's elderly asthma patient declares that hunger has driven the rodents to die in the open by the hundreds. A young journalist, Raymond Rambert, calls on Dr. Rieux to discuss his current project, a report on the sanitary conditions in the Arab population. Dr. Rieux's main concern before talking with Rambert is to make sure that Rambert will report the truth about the sad state of public sanitation.
Dr. Rieux's mother comes to stay with him while his wife is away. Meanwhile, Dr. Rieux contacts Mercier, the man in charge of pest control, to suggest that sanitation measures be taken. The public begins to feel uneasy when the flood of dying rats continues to increase. The newspapers clamor for the city government to address the problem. In response, the city arranges for the daily collection and cremation of the corpses. Just as a mild hysteria begins to grip the public, the phenomenon abruptly disappears.
The same day, Dr. Rieux meets Father Paneloux, a Jesuit priest, escorting a feverish, weakened M. Michel to his home. M. Michel's neck, armpits, and groin are swelling painfully. Dr. Rieux promises to visit him later in the afternoon. Meanwhile, he receives a telephone call from a former patient, Joseph Grand, regarding an accident suffered by his neighbor, Cottard. Upon his arrival, Dr. Rieux discovers that Cottard has tried to hang himself. Cottard becomes agitated when Dr. Rieux states that he will have to submit a report about the incident to the police. Dr. Rieux visits M. Michel to find his condition worsening. M. Michel dies in an ambulance en route to the hospital.
Other victims succumb to the same illness in the days that follow. The narrator introduces the reader to Jean Tarrou, the author of the written documents mentioned earlier. Tarrou, a vacationer in Oran, keeps notebooks containing detailed reports of his observations about daily life in Oran. He records conversations regarding the appearance of the mysterious illness in the wake of the dying rats. An old man periodically comes out onto a balcony opposite Tarrou's hotel room to spit on the cats sunning themselves below. When the plague of dead rats entices the cats away, the little old man seems greatly disappointed. Tarrou writes about a family of four with a disagreeable, strict father, M. Othon, who dines every day at the hotel. The hotel manager, dismayed at the dead rats in his three-star hotel, takes no comfort in Tarrou's assurance that everyone is in the same boat. The manager snootily explains that he is bothered precisely because his hotel is now like everyone else. One of the chambermaids becomes sick with the strange illness, but the manager assures Tarrou that it probably isn't contagious. In the midst of these vignettes of daily life in Oran, Tarrou ponders philosophical matters such as how not to waste one's time.
At the end of The Plague, the narrator reveals himself as Dr. Rieux. Perhaps Dr. Rieux withholds his identity because he is concerned with maintaining his objective distance from the chronicle. Because he defines The Plague as a chronicle, one would expect a journalistic report of the facts. Considering Camus's ideas about the impossibility of reaching an objective truth, it is not possible to agree with Dr. Rieux's assessment of his own document. Furthermore, despite Dr. Rieux's claims of objectivity, his description of pre-plague Oran society is heavily laced with irony. Rieux states that the spirit of pre-plague Oran is one of empty commercialism. The lives of Oran's people are entirely circumscribed by their habits. Every day, they follow the same routines of work, movies, cafes, and shallow love affairs.