Cardenio is set in sixteenth century Spain, in Andalucia, and the Sierra Morena Mountains.
Cardenio is in love with his childhood sweetheart, Luscinda. Her father Don Bernardo insists that Cardenio's father gives his approval of their relationship, before allowing it to continue any further.
Because of his skill in horsemanship, Cardenio is called to Court to be the companion of Fernando, the Duke's wild younger son.
Fernando is passionately obsessed with a wealthy farmer's daughter called Dorotea. After seducing her with promises of marriage, he abandons her and sets his sights on Luscinda, although she is betrothed to his best friend.
Fernando sends Cardenio back to court so he can pursue Luscinda unhindered. Her father is happy to accept such a wealthy young aristocrat as a husband for his daughter, and a marriage is arranged. Luscinda sends in secret for Cardenio, who rushes back to try and stop the wedding. Unable to prevent it, Cardenio is driven mad with grief and rage and disappears into the mountains.
Dorotea has dressed herself as a boy in order to pursue Fernando, and is living with the shepherds in the mountains when she encounters Cardenio in his madness.
Fernando, determined to pursue Luscinda, flees, discovers that having fled her home she has taken refuge in a convent, and intends to abduct her. Pedro, Fernando's older brother, agrees to help, and in order to resolve the matter, brings all the parties together in an inn, where Fernando is brought face to face with the wronged Dorotea. The couples are finally reunited.