Anselmo and Lothario, well-born young gentlemen of Florence who are known to all as The Two Friends, maintain their close relationship even after Anselmo's marriage to Camilla, a beautiful, rich, devoted, and virtuous maiden. Having such successful relationships with wife and friend, Anselmo is discontented with a malaise that increases each day. "I have an immense desire," he tells the shocked Lothario, "to test Camilla's virtue. I can never value one who owes her virtue to lack of opportunity, rather than to a vigorous denial of an aggressive and persistent lover." Anselmo begs his friend to act as Camilla's tempter, promising to ask someone else to do the job if Lothario should refuse. The husband then takes an out-of-town business trip in order to provide the opportunity for the plan. Despite his reserved behavior, Lothario falls so much in love with Camilla that he begins a sincere courtship. Camilla repulses him immediately and writes a letter to her husband.
Camilla's letter, urging her husband to return home and protect for himself what his best friend now pursues, receives a cool reply. She resolves to trouble her husband no longer and to face the matter herself. Unable to withstand the ardent Lothario, Camilla surrenders with all her heart, sharing the secret only with her maid Leonela. When Anselmo returns home a few days later, he begs his friend for the news of his fate. Lothario assures him that no wife is more virtuous or more resolute than Camilla. Still dissatisfied, the husband asks his friend to continue acting as seducer just to make sure, and he continues to provide ample opportunity for the test.
Meanwhile, Leonela has been getting bolder about the conduct of her own affair with a young man from town. One day Lothario sees this unknown fellow leave the house. Imagining that Camilla entertains another lover, he jealously seeks out Anselmo, telling him that his wife is now ready to surrender her virtue and that the husband must come to witness secretly her faithlessness. For her part, Camilla is so upset with her maid's indiscretion that she asks Lothario for advice, and the young man is remorseful for his jealousy and explains what he has done. But Camilla assures him that she has an excellent plan. Knowing full well that her husband is a secret witness, Camilla and Leonela stage a mock tragedy. The wife would rather die than stain Anselmo's honor. Stabbing herself, though in a place where the wound will do no harm, Camilla makes her husband believe in her unimpeachable virtue and in the faith of his friend, and he is again a satisfied and happy man.