Posthumus's account of the means whereby the British gained the victory (V. iii. 3–58) is taken from Holinshed's Chronicles of Scotland, which describe the sudden defeat of the Danes by the Scots, in the year 976, through the intervention of a husbandman named Hay, and his two sons.
The plot of Boccaccio's novel may be summarized as follows: Bernabo Lomellino of Genoa, stopping at an inn in Paris, boasts of his wife's virtue and devotion. Ambrogiuolo of Piacenza sneers at woman's virtue, and proves by philosophical argument that all women must be unchaste. Man is not chaste; woman is more frail than man; ergo! Entreaty, flattery, and gifts will win any woman. Bernabo repudiates philosophical argument and reaffirms his faith in his wife, Ginevra. The discussion waxes hot. Bernabo, in his anger, wagers his head against a thousand florins that Ambrogiuolo could not tempt Ginevra to sin. Ambrogiuolo accepts the wager, substituting a sum of money for Bernabo's head, and starts for Genoa. Within three months he must return with indisputable proofs of his triumph over Ginevra's virtue. Just as he is despairing of success he meets a poor woman, to whom Ginevra has been kind, and bribes her to send him into Ginevra's chamber, in her chest, on the pretence that she is about to take a journey and wishes to leave her belongings in Ginevra's care. Night comes; he emerges from the chest, notes the situation of the room, its ornaments and pictures, and approaching the bed he admires the lady's beauty and perceives the mole on her left breast. For further evidence he removes a gown, a ring, and a girdle. Bernabo is not moved by the description of the room, nor by the articles of apparel, but is 'struck to the very heart' when Ambrogiuolo reveals his knowledge of the mole. He sets out for home 'most cruelly incensed against his wife,' and sends ahead a servant with a letter
