Miguel de Cervantes, aging and an utter failure in his varied careers as playwright, poet and tax collector for the government, has been thrown into a dungeon in Seville to await trial by the Inquisition for an offense against the Church. There he is hailed before a kangaroo court of his fellow prisoners: thieves, cutthroats and trollops who propose to confiscate his meager possessions. One of these possessions is the uncompleted manuscript of a novel called "Don Quixote," and Cervantes, seeking to save it, proposes to offer a defense in the form of an entertainment. The "Court" accedes, and before their eyes, donning makeup and costume, Cervantes and his faithful manservant transform themselves into Don Quixote and Sancho Panza, proceeding to play out the story with the involvement and participation of the prisoners as other characters.
   Quixote and Sancho take to the road, singing MAN OF LA MANCHA ("I, Don Quixote") in a campaign to restore the age of chivalry, to battle evil and right all wrongs. The famous encounter with the windmills follows, but Quixote ascribes his defeat to the machinations of his enemy, the dark enchanter, whom one day he will meet in mortal combat. While Quixote and his squire are en route to a distant roadside inn - which the don insists to Sancho is really a castle - Aldonza, the inn's serving-girl and part-time trollop, is propositioned and taunted by a group of rough muleteers and replies that "one pair of arms is like another," IT'S ALL THE SAME. Upon arrival at the inn, Quixote, in his splendid if lunatic vision, sees Aldonza as the dream-ideal whom he will worship and serve evermore, DULCINEA. Aldonza is confused and angered by Quixote's refusal to recognize her for what she really is.                             
   In the country home which Quixote left behind, his niece Antonia and his housekeeper seek out the neighborhood Padre to consider how this madness may best be dealt with. However, the Padre finds that their concern is more with embarrassment to themselves than with the welfare of Quixote as the three sing I'M ONLY THINKING OF HIM. The Padre and Dr. Sanson Carrasco, Antonia's fiance, are delegated to pursue the madman and bring him back home. Meanwhile, Quixote dispatches Sancho to Aldonza with a "missive" declaring his everlasting devotion to Dulcinea. Adonza, being even more confused, questions Sancho as to why he so faithfully follows Quixote. Sancho replies, simply, I REALLY LIKE HIM.                  
   While Quixote is standing vigil in the courtyard of the inn in preparation for his official dubbing as a knight, Aldonza asks, WHAT DO YOU WANT OF ME? The muleteers tease and taunt her with the song LITTLE BIRD, LITTLE BIRD. Quixote encounters an itinerant barber wearing his shaving basin as a hat to ward off the sun (THE BARBER'S SONG). The knight confiscates the shaving basin in a comic interlude, convinced that it is the miraculously protective GOLDEN HELMET of Mambrino and is ceremoniously crowned with the aid of the muleteers and the incredulous barber who comes to believe that his basin may, indeed, be the celebrated helmet.
   The Padre and Dr. Carrasco, having failed in their mission, grimly plan a new attempt to bring Quixote to his senses. The Padre hopes that "The cure will not prove worse than the disease" (TO EACH HIS DULCINEA).
   At this point, replying to Aldonza's question about doing the things he does, Quixote explains his credo in THE IMPOSSIBLE DREAM ("The Quest"). Following the Padre's and Dr. Carrasco's departure, Quixote defends Aldonza's honor in a successful battle with the muleteers (THE COMBAT), and as his reward is formally knighted by the Innkeeper in THE DUBBING.
   Now, having caught the fever of Quixote's idealism, Aldonza attampts to put it into practice, but for her efforts she is cruelly beaten and carried off by the muleteers (THE ABDUCTION). Disillusioned, Aldonza passionately denounces Quixote and his dreams, which have brought her only anguish (ALDONZA). Now appears "The Enchanter," fantastically costumed as The Knight of The Mirrors. He challenges Quixote, forcing him to look into the mirror of reality where Quixote sees reflected a fool and a madman. Quixote is defeated.. .but Aldonza, a witness to his destruction, feels a deep sense of loss. The Knight of the Mirrors reveals himself as Dr. Carrasco.
   At home again, the old man who once called himself Don Quixote is dying. Sancho attempts to cheer him up with A LITTLE GOSSIP. Aldonza, having followed, forces her way into the room pleads with him to become Don Quixote once more and restore the vision of glory she held so briefly. Poignantly, she urges him to remember that he once called her by another name, DULCINEA. As she helps him recall the words of "The Quest," Quixote, stirred to the old fire, rises from his bed, calling for his armor and sword so that he, Sancho, and Aldonza may once more set out upon their mission. But in the moment of reaffirmation, during a reprise of MAN OF LA MANCHA, he collapses. While the Padre, who has been at Quixote's bedside, sings THE PSALM over the lifeless body, Aldonza, having seen the vision once more, refuses to acknowledge Quixote's death. "A man died. He seemed a good man, but I did not know him," she contests, "Don Quixote is not dead." When Sancho questions her, she replies, "My name is Dulcinea." Quixote, having considered her throughout an individual of unique worth and value, has transformed her.
   Back in Cervantes' dungeon, the prisoners have been deeply affected by his story and restore to him his precious manuscript. As he leaves to face his real trial, they unite to sing the words of Cervantes - Quixote's THE IMPOSSIBLE DREAM.