Don Mendo, Marquess of Cabra, gallant and dashing knight of medieval Castilian, is also a virtuous mandoline player and a specialist in climbing towers. But he has a bad run, all played and all lost at seven-thirty (card game), and lost his honor playing in his latest escalation of love to the apartment of his beloved and beautiful Magdalena. Don Nuño Manso de Jarama, father of Magdalena, has pledged the hand of his daughter to the Duke of Toro, and surprises Don Mendo in the room of Magdalena. To save the honor of his beloved one, Don Mendo says that no love has led him to the Tower, but he has climbed to steal. Magdalena is clean of all suspicion, and he is condemned to die buried in the castle wall. The Marquess of Moncada and other noble gentlemen, all friends of Don Mendo, facilitate his escape.

Cuando Don Mendo, marqués de Cabra, galante y audaz caballero medieval, escala un torreón para llegar a los aposentos de la bella Magdalena, es sorprendido por Don Nuño Manso de Jarama, el padre de la dama, que ha concedido la mano de su hija al Duque de Toro. Para proteger el honor de su amada, Don Mendo asegura que ha subido al torreón para robar, por lo que es condenado a morir emparedado vivo. El Marqués de Moncada y otros nobles caballeros, amigos todos de Don Mendo, le facilitan la huida. Ha pasado el tiempo y Magdalena sigue siendo tan infiel al de Toro como antes al de Cabra. Ahora es la amante del Rey. Un 'bellísimo' trovador, que no es otro que Don Mendo, aparece en el campamento del Rey y enamora a todas las mujeres. El de Toro y el de Manso acuden a la Cueva de Algodor, lugar de cita de todos los enamorados, al acecho de la infiel.