The mayor, or the “Podesta,” is much taken with his new gardener Sandrina to the chagrin of his jealous housekeeper Serpetta. However, Sandrina is actually the Marchioness Violante in disguise, searching for her lover Belfiore, who a year ago stabbed her in a fit of jealousy and fled, believing her dead. Violante’s servant Roberto, posing as Sandrina’s cousin Nardo, is working as the Podesta’s manservant and has fallen for Serpetta.

Arminda, the Podesta’s niece, has meanwhile spurned her admirer Ramiro for a new, aristocratic suitor. Sandrina is distraught to discover that this new suitor is none other than her own errant lover, Count Belfiore. When Belfiore arrives, he realizes that Sandrina is actually Violante, but she refuses to admit her true identity. Arminda senses that something is awry and fears losing Belfiore to Sandrina, which rekindles Ramiro’s hope of winning Arminda back.

After dismissing Ramiro, Arminda confronts Belfiore about Sandrina, while Nardo woos Serpetta in vain. Sandrina con­tinues to deny that she is Violante, and goes so far as to tell Belfiore that she witnessed the marchioness’s death. When Ramiro produces an arrest warrant accusing Belfiore of murder, Sandrina finally confesses the truth. But left alone with Belfiore, she claims that her admission was merely a ruse to save him from arrest, and his confusion drives him to increasing despair.

Her marriage to Belfiore threatened, Arminda has Sandrina abducted and left to die in the nearby forest. Nardo discovers what Arminda has done and leaves to search for Sandrina, followed by the others. As night falls over the woods, a terri­fied Sandrina takes shelter in a cave. The searchers arrive in separate groups, unbeknownst to each other, and in the dark­ness identities are mistaken and chaos ensues. Unable to cope with their tortured and confused feelings for each other, Belfiore and Sandrina retreat into madness as the others watch in horror.

Sandrina and Belfiore awaken at dawn, their senses restored, and decide that they must never part. Arminda gives in to Ramiro and agrees to marry him, while Serpetta accepts Nardo’s advances. Only the Podesta is left alone, hopeful that another Sandrina will one day cross his path.