The household of Leonato, Governor of Messina, awaits the arrival of the victorious soldiers Don Pedro, Claudio and Benedick. Leonato’s niece Beatrice makes sarcastic remarks about Benedick. When he and the two others arrive, she and Benedick begin trading insults, each boasting that they are hard-hearted, and immune to the charms of the opposite sex.
Claudio tells Benedick he is in love with Leonato’s daughter Hero. Benedick mocks him, and tells Don Pedro all about it as soon as he enters the room. Don Pedro comes up with a plan to disguise himself as Claudio, and woo Hero for him at that evening’s masked dance. Meanwhile, Benedick scoffs at love and marriage—but Don Pedro swears that Benedick will fall in love before long.
Leonato’s brother Antonio learns that Claudio loves Hero, and informs his brother. At the same time, Don Pedro’s bastard brother Don John—defeated enemy in the war before the play—learns from his minion Borachio of Don Pedro and Claudio’s plans. They scheme to ruin things at the dance that night.
As they prepare for the dance, Leonato, Beatrice and Hero discuss Hero’s marriage and marriage in general. Beatrice explains why she does not want to wed. The party-goers arrive, and Don Pedro—disguised as Claudio—goes off to propose to Hero. Meanwhile, a disguised Benedick is insulted by Beatrice, who pretends not to recognize him, and calls him a “dull fool.” Benedick gets angry, and goes off alone. Elsewhere in the crowd, Don John and Borachio pretend to mistake Claudio for Benedick, and convince him that Don Pedro wants Hero for himself. Claudio is upset until Don Pedro arrives with an announcement: Hero has agreed to marry Claudio. The wedding is set for a week later, and in the meantime, Don Pedro proposes that everyone try to make Benedick and Beatrice fall in love.
Borachio and Don John make a new plan to ruin the announced marriage. They scheme to trick Claudio and Don Pedro into thinking Hero has been unfaithful, by arranging for the two to see Borachio and Margaret—Hero’s waiting-gentlewoman—having sex through Hero’s window.
Unaware of Borachio and Don John’s plan, Don Pedro and his friends enact their own plant to make Benedick fall in love. Benedick, alone in Leonato’s garden, runs and hides when he sees Don Pedro, Leonato, Claudio and Balthazar approaching. Knowing Benedick is there, they speak somberly about Beatrice’s love for Benedick. Benedick is quickly convinced, and when Beatrice comes to fetch him for dinner, he reads flirtatious double meanings into her words. Later, Hero, Margaret and Ursula lay the same trap for Beatrice, who is as easily convinced.
Soon after, Don John convinces Claudio and Don Pedro that Hero has been unfaithful. They agree to come watch her window for signs of a lover, and plan to shame her at her wedding if the accusations are true.
Dogberry, the head of the town Watch, and Verges, his second-in-command, instruct the members of the night watch. As this is going on, the watchmen overhear Borachio bragging to Conrade about how he made love to Margaret and convinced Don Pedro and Claudio of Hero’s unfaithfulness. The Watch arrests arrest both men. Just before the wedding the next morning, Dogberry and Verges try to bring Leonato to interrogate the conspirators. But Dogberry has so much trouble making himself understood that Leonato dismisses the pair, telling them to do the examination themselves.
The wedding proceeds. Just as the Friar is asking if anyone has any objections to the marriage, Claudio and Don Pedro make their accusation, humiliating Hero and causing her to faint from shame. Claudio, Don Pedro and the guests leave, and Leonato is beside himself. The Friar, doubting the accusations, suggests that Leonato pretend Hero is dead. This will give them time to look into the accusations, and perhaps to change Claudio’s feelings as well. Leonato agrees, while Benedick and Beatrice swear themselves to secrecy. Outraged by what has happened to her cousin, Beatrice asks Benedick to kill Claudio, saying that she cannot love him if he won’t. After some initial hesitance about fighting his best friend, he agrees.
Dogberry and the watch clumsily interrogate Conrade and Borachio. Despite Dogberry’s misuse of words and obsession minor matters—such as when Conrade calls him an ass—they extract a confession, and plan to bring the criminals to Leonato’s.
A fight almost breaks out between Leonato and Claudio, joined by Antonio and Don Pedro. Benedick arrives, and puts an end to the fight by challenging Claudio to fight him the next day. Don Pedro and Claudio do not take him seriously at first, but eventually decide that his love for Beatrice has driven him to do it. As they discuss Benedick’s change and challenge to Don Pedro, Dogberry, Verges and the Watch arrive with Conrade and Borachio, who confesses to the deception. Horrified, Claudio and Don Pedro beg Leonato’s forgiveness. Leonato agrees to forgive Claudio if he will hang an epitaph on Hero’s grave, clear her reputation, and then marry his niece.
Benedick tells Beatrice that he has agreed to fight Claudio. Ursula, a lady of the household, brings the news that Don John’s treachery has been discovered, and that he has fled from Messina.
Don Pedro and Claudio go to Hero’s grave to hang an epitaph. Afterward, they proceed to Leonato’s for the wedding. There, Claudio is presented with Leonato’s niece, who is wearing a mask. To his surprise, when the mask is removed the “niece” turns out to be the still-living Hero. Claudio is overjoyed. Meanwhile, Benedick unmasks Beatrice, whom he has been given permission to marry. Just before they do, they realize that they were tricked into falling in love by the others. They decide to marry anyway, and Benedick calls for dancing before the weddings.