The action of Much Ado About Nothing occurs during several days of a visit by Don Pedro, Prince of Aragon, and his followers at the large estate of Leonato, Governor of Messina. Don Pedro has been victorious in a small war against his own half-brother, Don John, who has now (reluctantly) joined him.
From the beginning to the end of the play, two love stories are intertwined. One story follows the formal, romantic relationship between Leonato's daughter, Hero (a young woman), and Claudio (a young officer): Claudio realizes, after returning from war, that he is deeply in love with Hero and wants to ask her father for permission to marry her. His commander, Don Pedro, helps Claudio propose marriage, with some momentary confusion about who the suitor is — Don Pedro or Claudio.
The other couple, Beatrice (Hero's cousin) and Benedick (another officer), work hard to give the impression that neither is the least bit interested in the other, still smarting over bad experiences in earlier encounters with one another. From the beginning of the play, Beatrice and Benedick tease and insult one another mercilessly and repeatedly deny that they will ever marry anyone, let alone marry one another. However, the audience can tell almost immediately that they don't entirely believe their own disclaimers. Their friends arrange for them to overhear conversations revealing how much each is loved by the other.
Meanwhile, the defeated Don John, a self-proclaimed villain, is eager to carry out serious mischief against his brother and Claudio, who helped defeat him. One of John's men enacts a scene at Hero's window in which a woman who appears to be Hero succumbs to the amorous attentions of a man other than Claudio. John further arranges for Claudio and Don Pedro to observe this scene. As a result of seeing this apparent deception, Claudio angrily denounces Hero during their wedding ceremony and, with Don Pedro, storms off as the deceived husband-to-be. The friar performing the ceremony comforts Hero, her father, and the other couple (Benedick and Beatrice), and arranges for Hero to be hidden as though dead, until Claudio regains his senses. Beatrice's defense of Hero after her denouncement unites Beatrice and Benedick in the cause of Hero's revenge, and they declare their love for one another.
In the meantime, Dogberry (a comically bumbling constable) and his men on night watch stumble on the conspiracy against Don Pedro and arrest John's men, who confess their guilt under questioning.
Soon Claudio is forced to admit his error in thinking that Hero would deceive him and, believing her dead, mourns for her and agrees to marry one of Hero's cousins. The cousin turns out to be a disguised and forgiving Hero. Beatrice and Benedick are also to be married. Don John tries to run off but is recaptured.