The virile and well-endowed Lidio is discovered by Duke Ferruccio in the bedroom of his wife Lucrezia, and put in the pillory. During the punishment, he bets with the duke himself that he will succeed in seducing Fulvia, the young bride of the wealthy old man Calandro, within a month, at the cost of his genitals. At the same time, he is exiled from the city for precisely thirty days, so he disguises himself as a court lady and manages to enter Calandro's house, being hired to teach Fulvia the art of seducing her old, impotent husband and thus be able to procreate. He succeeds in bedding the bride and also the maid. Calandro, however, falls in love with the fake lady-in-waiting and does everything he can to seduce her. In order to deceive the old man and not be thrown out of the house, Lidio decides to play along, pretending to love Calandro.
The latter, disguised as a woman and convinced he will be invisible thanks to the help of the alchemist Ruffo, secretly meets Lidio. Fulvia pretends to discover her husband's secret affair and improvises a scene in which Calandro is battered by the two. In his escape, Calandro is attacked by two drunks who rape him; Lidio and the corrupt alchemist make him believe he is pregnant. Lidio, however, is imprisoned by Ferruccio after a brutal prank and hung by his testicles on tiptoe; exhausted, Lidio succumbs to fatigue and is castrated; finally, he is forced to perform the only thing he is good at: singing in the church boys' choir.