A teacher name Can returns to his native land of Andorra, bringing with him a baby called Andri whom he rescued from the “Nation of The Blacks,” where the baby would have been at risk of antisemitic violence. The play’s action begins a number of years after this event, with Andri grown to manhood and in love with his half-sister, Barblin, who is Can’s daughter. The opening scene shows Barblin whitewashing her father’s house in preparation for what she expects to be her wedding to Andri, whose love she warmly reciprocates. However, she is accosted during her work by a bitter soldier known as Pieder, who warns her that underneath the whitewash, there will always be blood-red clay.

This warning proves to be a telling metaphor for Andorra itself and for the people in the town where Barblin and Andri live, who, while seeming virtuous and pure on first appearances, soon turn out to harbor the same unfortunate antisemitic views as were pervasive in the “Nation of Blacks.” During their conversations at the local inn, the townspeople ascribe to Andri stereotypical Jewish traits, portraying him as a greedy, manipulative capitalist. The local cabinet-maker is afraid that Andri will prove a more adept salesman than him because of his Jewish faith, and so he demands an unreasonably high price for taking him on as apprentice. Andri grudgingly accepts the identity foisted on him by his neighbors, though he finds it hard to swallow when his foster father refuses to let him marry Barblin, believing that it is because of his religion.

One night, Barblin is sexually assaulted by Pieder while lying in bed, with her former fiancé sitting right outside the door. In the morning, Can approaches his foster son hoping that the alcohol he has consumed the night before will embolden him to tell him the truth about his heritage, but he struggles to get the words out, and Andri isn’t ready to wait and listen. Andri knocks on Barblin’s door to wake her and is surprised by Pieder, who opens the door and instructs him to go away, threatening him with violence if he doesn’t do so. Andri visits a priest the next morning, who tries to help him reconcile himself to being different from the Andorrans, but Andri continues to struggle with this idea.

He angrily confronts Pieder and his friends in the town square concerning the incident with Barblin, but he is soundly beaten, ultimately requiring rescue from a passing woman, The Señora, who is a native of the “Nation of The Blacks.” After helping Andri recover from his injuries, she confronts Can, accusing him of cowardliness for not telling his foster son the truth about his past. The friendship between Andri and The Señora is short-lived, since she is killed by an unknown Andorran. Andri is blamed for this crime by the innkeeper, though he had a sound alibi, having been in conversation with the priest at that time (with the latter on this occasion trying to convince him that he was, in fact, the true son of Can, though again Andri is unconvinced).

The Blacks invade Andorra, seeking retribution for their murdered citizen, and they force all the men to walk blindfolded across the town square. “The Jew Detector” is of the opinion that Andri is guilty for the crime, and despite Can’s belated insistence that Andri is not a Jew, he is executed by The Blacks. The play’s cyclical structure is concluded with the image of Barblin, obsessively whitewashing her father’s house in a symbolic effort to erase the painful knowledge of her father and her half-brother’s death—the former’s by suicide.