It is the 1940s in French-occupied Algerian.. Dr. Bernard Rieux is the first to intuit that things are not right with the city when he notices a sudden spike in the number of dead rats around town. Before too long thousands are making their way to the streets to die. The sight of the Oran littered with the carcasses of rats stimulates panic among the citizens and forces the government to order a special force tasked with cremating the rodents.
As the rat carcass problem begins to be contained, Dr. Rieux is called to treat the concierge where he works who complains of an unusual fever. Not long after the concierge succumbs to the ravages of fever, doctors all over town are flooded with patients experiencing similar symptoms. Rieux and an elderly colleague named Castel suspect the Oran has become the victim of an outbreak of bubonic plague. Request to the government to initiate a strategy before an epidemic gets out of control are ignored and only after the death toll skyrockets are leaders finally incapable of denying the seriousness of the situation.
By the time they finally respond to the gravity of the outbreak, the only choice is absolute quarantine of the city. Oran essentially becomes cut off and isolated from the rest of the world.
The reaction of the residents of Oran vary widely in terms of specifics, but share a commonality of theme: it is the sense of imposed exile from society and the longing for simple human contact with friends and family outside the closed gates that drives every individual response. Permeating throughout the fears of the disease and the longing and loneliness is a distinct exhibition of belief that the singling out of their city is no random act of science, but divine punishment of some kind. Helping to foster this belief is Father Paneloux whose sermons are filled with stern Jesuit reasoning that Oran has committed sins so great that simple forgiveness is not warranted.
A Parisian journalist unlucky enough to happen to be in the city when the outbreak begins isn’t buying this and is determined to escape back home to reunite with his wife. His attempts are foiled by the ineptitude of both the government and the underground. A paranoid criminal named Cottard attempts to aid Rambert in his escape. Alone among those trapped inside, Cottard is actually glad to see what effects the plague is having on the town. Suddenly, everyone is just as lonely and afraid as him. Not only that, he is making a killing in the booming business of smuggling that is another consequence of the epidemic.
Another visit who got trapped by bad timing is Jean Tarrou and he has been carefully making notes of everything he’s observed relating to the plague. Those observations stimulate him to organize sanitation duties with the help of volunteers. Meanwhile, just as Rambert is as about ready to put his escape strategy to the test, he learns that Dr. Rieux—who has been the leading figure in trying to fight the plague—has a wife on the outside experiencing her own medical quarantine as a patient being treated in a sanatorium. The sacrifice being made by Rieux inspires Tarrou to give up on his plan to escape and stay to fight the epidemic.
The initial self-centered response of individuals to the quarantine as a personal tragedy eventually gives way to a widespread realization that everyone is affected equally even if in starkly different ways. The acceptance of the plague under these terms lessens the selfishness of the town, but does little to alleviate the collective disconsolation and hopelessness. Adding to the despair is a death toll affecting so many people that cremation is necessary to keep up. When the young child of Oran’s magistrate succumbs to the suffering and perishes, Father Paneloux is moved to get another sermon.
The theme of this sermon is plainly put: the plague is evidence enough that you either believe in Christianity wholeheartedly or you reject it outright. Not long afterward, Paneloux himself dies, but without manifesting any symptoms of the disease raving the population. In contrast to Paneloux, others who have shown victims begin to make miraculous recoveries and avoid death. At that point, Tarrou finally is diagnosed, but fails to recover and dies. He has become the exception, however, and soon the town is barely containing its desire to celebrate the evidence that the plague is diminishing and will soon disappear.
Along among the quarantined not bursting with happiness at this thought is Cottard. On the day the gates to the town finally reopen, his madness finally overcomes him and he takes to the street randomly firing his gun until the police arrest him. The long-awaited reunion between Rambert and his wife takes place not back home in Paris, but in Oran. Dr. Rieux is not so lucky; his wife has died during the separation mandated by the quarantine. Flush the freedom to do whatever they want, the residents of town do little more than go back to their lives as they were before the plague arrived under the awareness that acting like everything is the same is an utter pretense.
The unidentified narrator of these events finally reveals himself as the tale draws to a close. The chronicler was Dr. Rieux and his book was composed as a testament to the victims and those who fought it rather than as his own self-serving story as a personal victim of the tragedy. An attempt is made to end the story on an inspirational note with his observance that ultimately those trapped in Oran revealed the better side of human nature more often than the worst. That note of optimism is undercut by his haunting reminder that the microbe responsible for bubonic plague can lie dormant for so long that it creates the illusion of being gone forever when in reality, it has the power to spread into an epidemic with little warning.