Don Pedro, prince of Medina (Denzel Washington
), his resentful brother Don John (Keanu Reeves
), and his noblemen Claudio (Robert Sean Leonard
) and Benedick (screenwriter/director Kenneth Branagh
) return from war, ready for merriment and love. Claudio loves Hero (Kate Beckinsale
), the young daughter of the nobleman Leonato (Richard Briers
), but Benedick hates Beatrice (Emma Thompson
), Leonato's beautiful, witty, but sharp-tongued niece, who hates him back.
Claudio and Hero are soon engaged; as they prepare for their wedding, they decide, with the help of Don Pedro, to trick Benedick and Beatrice into confessing their true love for each other. The plan works without a hitch, but trouble comes in the form of Don John, who is jealous of his brother's power and of his affection for Claudio. Don John devises a scheme where one of his lieutenants will make love to Hero's maid Margaret (Imelda Staunton
) at Hero's window the night before the wedding--and call her Hero. Don John takes Don Pedro and Claudio to Leonato's house, where they see the encounter and are convinced the woman is Hero. The next day Claudio disgraces Hero publicly at the wedding and refuses to marry her. She faints and Leonato is persuaded to pretend that she is dead until the situation is sorted out.
The foolish warden Dogberry (Michael Keaton
) manages to arrest Don John's lieutenants and they confess to the plot. Claudio is crushed when he learns that he killed Hero with his false accusations. He begs Leonato to punish him and Leonato tells him his punishment is to marry his (other) niece, who closely resembles Hero. Claudio agrees but first spends a night mourning for Hero and proclaiming her innocence. Don John escapes Medina. The next morning Claudio marries the supposed niece, who removes her veil to reveal that she is Hero. They are very happy but Benedick and Beatrice almost break up when they discover they were tricked into admitting their love. In the end, Don John is arrested and brought back to face punishment, Benedick and Beatrice marry, and all dance around Leonato's garden singing "Noddy noddy."