The war is over. Pedro Prince of Aragon, with his followers Benedick and Claudio, visits Leonato, Duke of Messina, father of Hero and uncle of Beatrice.
Claudio falls in love with Hero and their marriage is agreed upon. Beatrice and Benedick despise love and engage in comic banter.
The others plot to make them fall in love with each other, by a trick in which Benedick will overhear his friends talking of Beatrice's supposed secret love for him, and vice versa.
Meanwhile Don John, the prince's misanthropic illegitimate brother, contrives a more malicious plot with the assistance of his follower Borachio: Claudio is led to believe that he has witnessed Hero in a compromising situation on the night before her wedding day – in fact it is her maid Margaret with Borachio.
Claudio denounces Hero during the marriage ceremony. She faints and on the advice of the Friar, who is convinced of her innocence, Leonato announces that she is dead. Beatrice demands that Benedick should kill Claudio.
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The foolish constable Dogberry and his watchmen overhear Borachio boasting of his exploit and the plot is exposed.
Claudio promises to make amends to Leonato: he is required to marry a cousin of Hero's in her place. When unmasked, she is revealed as Hero. Beatrice agrees to marry Benedick.