Act I
The play starts in the town square of a small provincial French village. Two friends meet at a coffee shop: eloquent, intellectual and prideful Jean, and the simple, shy, kind-hearted drunkard Bérenger. They have met to discuss an unspecified but important matter. Rather than talk about it, Jean berates Bérenger for his tardiness and drunkenness, until a rhinoceros rampages across the square, causing a commotion. During the discussion that follows, a second rhinoceros appears and crushes a woman's cat. This generates outrage and the villagers band together to argue that the presence of the rhinoceroses should not be allowed. A discussion about whether they saw two different rhinoceroses or the same one twice leads to a heated argument between Bérenger and Jean, eventually causing Jean to walk away in a huff.
Act II
Bérenger arrives late for work at the local newspaper office. Daisy, the receptionist, with whom Bérenger is in love, covers for him by sneaking him a time sheet. At the office, an argument has broken out between sensitive and logical Dudard and the violent, temperamental Botard. The latter does not believe a rhinoceros could appear in France.
Mrs. Bœuf (the wife of an employee) says that her husband is unwell and that she was chased all the way to the office by a rhinoceros. Botard scoffs at the so-called "rhinoceritis" movement and says that the local people are too intelligent to be swayed by empty rhetoric. A rhinoceros arrives and destroys the staircase that leads out of the office, trapping all the workers inside. Mrs. Bœuf recognizes the rhinoceros as her husband, transformed. Despite a warning, she joins him by jumping down the stairwell onto her husband’s back. Daisy has called the firemen. The office workers escape through a window.
Bérenger visits Jean in order to apologize for the previous day's argument. He finds Jean sick and in bed. They argue once more, this time about whether people can transform into rhinoceroses and then about the morality of such a change. Jean is at first against it, then more lenient. Jean begins to gradually transform. Finally, Jean proclaims that they have just as much of a right to life as humans, then says that "Humanism is dead, those who follow it are just old sentimentalists". After transforming fully, he chases Bérenger out of the apartment.
Act III
Bérenger is at home having a nightmare. He fears transforming like Jean, earlier. He has a sip of brandy and retires to bed. Dudard visits him and they have nearly the same exchange as with Jean earlier. Only this time, Dudard is accepting of the transformation and Bérenger resists the idea and defies that he will change.
Daisy arrives with a basket of love. Both Dudard and Bérenger desire her. Botard, Daisy reveals, has also changed. Many villagers, including firemen, have begun to transform. Dudard leaves, wanting to see firsthand. Bérenger tries to stop him. Dudard turns into a rhinoceros himself.
Bérenger laments the loss of Dudard. Daisy tells Berenger that they have no right to interfere in others’ lives. Bérenger says he will defend her. He blames both himself and Daisy for aiding, through lack of sympathy, the transformations of Jean and Papillon, respectively. Daisy allays his guilt.
The phone rings, but they hear only rhino trumpeting on the line. They turn to the radio for help, but the rhinos have taken that over, too. Bérenger professes his love for Daisy. She seems to reciprocate. They attempt to have a normal life amongst beasts. Bérenger suggests that they attempt to repopulate the human race. Daisy begins to move away from him, suggesting that Bérenger does not understand love. She has come to believe the rhinoceroses are truly passionate.
Bérenger slaps Daisy without thinking and then immediately recants. Bérenger exclaims that, "in just a few minutes we have gone through twenty-five years of married life!" They attempt to reconcile, but once more fight. As Bérenger examines himself in a mirror for any evidence of transformation, Daisy slips away to join the animals.
Now alone completely, Bérenger regrets his actions towards Daisy. In his solitude, he begins to doubt his existence. He attempts to change into a rhinoceros but cannot, then regains his determination to fight the beasts, shouting, "I'm not capitulating!"
