Warning: Wikipedia contains spoilers
The play centers around the fictional European town of Güllen (or Guellen, depending on the translation), which was once a vibrant center of culture but has in the past few decades decayed into near-bankruptcy. When the play opens, the town is preparing a celebration of the arrival of Claire Zachanassian, a former resident who had since attained a great fortune and is coming back to visit. She arrives with her fiancé (throughout the play, she has several husbands, and it is mentioned repeatedly that she has had many more), and after some general festivities on the part of the townspeople she announces the true reason she has visited: when she was young she was impregnated by her lover Alfred Ill, who, at the paternity suit, denied the charges and bribed two drunks to testify that they were the fathers, and she was shamed out of the town; now that she has become rich, she will give the town one billion marks if they kill Alfred Ill. The townspeople unanimously refuse to do so — but soon they start to buy things on credit, expensive things, even from Ill's own store. The townspeople's rhetoric of support behind Ill slowly but surely changes to flat-out outrage at his actions in his youth. Ill sees it all coming and accepts his eventual death, which is brought on by the crowd en masse. The mayor receives the check for the billion marks. The dark tone suddenly gives way to a prosperous, cheerful ending on behalf of the townspeople, which underscores the main themes of the play.
The play is written in a kind of resigned, slow manner that reflects the state of the town after their gradual ruin (which is revealed around the middle of the play to have been intentionally brought on by Zachanassian). There is a lot of potential in the play for varying interpretations, both in meaning and in production. It remains, nearly fifty years after its writing, a mainstay of Western theater.
The play was adapted as an opera libretto by the author and set to music by composer Gottfried von Einem, entitled Besuch der alten Dame and translated as The Visit of the Old Lady, and was first performed in 1971.
The plot was used for Kander and Ebb's musical The Visit, which received its first production at Chicago's Goodman Theatre in 2001.