The musical "The Man of La Mancha" is actually a play within a play, told in the setting of a dreary underground prison in 16th Century Seville, Spain. Miguel de Cervantes, a political prisoner of the Catholic Church during the days of the Inquisition, switches from author to foolish but daring old knight in an attempt to garner a defense of sorts. The prisoners decide to hold a mock trial in order to find Cervantes guilty and steal all his possessions (including a package he seems to value greatly). Cervantes presents a play as his defense, to give the "jury" insight into the "crimes" of which they accuse him - the crimes of being a tax collector and a poet.
The character of Alonzo Quijana, an old man, is a one of great imagination - he chooses to believe that he is a knight called Don Quixote, Knight of the Woeful Countenance, from the village of La Mancha. He is now a knight seeking to "right the unrightable wrong" in an era that has left knighthood and the principles it stands for far behind. Accompanied by his faithful servant, Sancho Panza, Quixote sings, "Whether I win or lose doesn't matter/it's how I follow the quest."
The prisoners are grudgingly taken in by the character of Quixote and the landscape of his imagination: they begin to see themselves in a new light. This is most true of the main female character, Aldonza, a prostitute Quixote calls Dulcinea and sees as a sweet virgin. When Aldonza begs the knight to see her as she really is, Quixote replies, "I've already seen you in my heart."
But when Quixote himself is ready to give up his visions and come back to Earth, he encounters his "unbeatable foe" - the Knight of Mirrors. He appears to Quixote and asks, "Do you see a gallant knight or an aging fool?" Confronted with the reality and absurdity of his situation, Quixote once again becomes Quijana, and his with his drive and will gone, he is stricken to his deathbed. It is Aldonza and faithful Sancho who convince him to continue to hold on to the "impossible dream."