Don Pedro, prince of Arragon, arrives in Messina accompanied by his bastard brother, Don John, and his two friends, the young Italian noblemen Claudio and Benedick. Don Pedro had vanquished his brother in battle. Now, reconciled, the brothers plan to visit Leonato before returning to their homeland. On their arrival in Messina, young Claudio is immediately smitten by the lovely Hero, daughter of Leonato, the governor of Messina. To help his faithful young friend in his suit, Don Pedro assumes the guise of Claudio at a masked ball and woos Hero in Claudio’s name. Then he gains Leonato’s consent for Claudio and Hero to marry. Don John tries to cause trouble by persuading Claudio that Don Pedro means to betray him and keep Hero for himself, but the villain is foiled in his plot and Claudio remains faithful to Don Pedro.
Benedick, the other young follower of Don Pedro, is a confirmed and bitter bachelor who scorns all men willing to enter the married state. No less opposed to men and matrimony is Leonato’s niece, Beatrice. These two constantly spar with one another, each trying to show intellectual supremacy over the other. Don Pedro, with the help of Hero, Claudio, and Leonato, undertakes the seemingly impossible task of bringing Benedick and Beatrice together in matrimony in the seven days before the marriage of Hero and Claudio.
Don John, thwarted in his first attempt to cause disharmony, forms another plot. With the help of a servant, he arranges to make it appear as if Hero is being unfaithful to Claudio. The servant is to gain entrance to Hero’s chambers when she is away. In her place will be her attendant, assuming Hero’s clothes. Don John, posing as Claudio’s true friend, will inform him of her unfaithfulness and lead him to Hero’s window to witness her wanton disloyalty.
Don Pedro pursues his plan to persuade Benedick and Beatrice to stop quarreling and fall in love with each other. When Benedick is close by, thinking himself unseen, Don Pedro, Claudio, and Leonato talk of their great sympathy for Beatrice, who loves Benedick but is unloved in return. The three tell one another of the love letters Beatrice had written to Benedick and had then torn up, and that Beatrice beats her breast and sobs over her unrequited love for Benedick. At the same time, on occasions when Beatrice is nearby but apparently unseen, Hero and her maid tell each other that poor Benedick pines and sighs for the heartless Beatrice. The two unsuspecting young people decide not to let the other suffer. Each will sacrifice principles and accept the other’s love.
Just as Benedick and Beatrice prepare to admit their love for each other, Don John is successful in his base plot to ruin Hero. He tells Claudio that he has learned of Hero’s duplicity, and he arranges to take him and Don Pedro to her window that very night to witness her unfaithfulness. Dogberry, a constable, and the watch apprehend Don John’s followers and overhear the truth of the plot, but in their stupidity the petty officials cannot get their story told in time to prevent Hero’s disgrace. Don Pedro and Claudio witness the apparent betrayal, and Claudio determines to allow Hero to arrive in church the next day still thinking herself beloved. Then, instead of marrying her, he will shame her before all the wedding guests.
All happens as Don John had hoped. Before the priest and all the guests, Claudio calls Hero a wanton and forswears her love for all time. The poor girl protests her innocence, but to no avail. Claudio says that he had seen her foul act with his own eyes. Hero swoons and lays as if dead, but Claudio and Don Pedro leave her with her father, who believes the story and wishes his daughter really dead in her shame. The priest believes the girl guiltless, however, and he persuades Leonato to believe in her, too. The priest tells Leonato to let the world believe Hero dead while they work to prove her innocent. Benedick, also believing in her innocence, promises to help unravel the mystery. Then, Beatrice tells Benedick of her love for him and asks him to kill Claudio and so prove his love for her. Benedick challenges Claudio to a duel. Don John had fled the country after the successful outcome of his plot, but Benedick swears that he will find Don John and kill him as well as Claudio.
At last, Dogberry and the watch get to Leonato and tell their story. When Claudio and Don Pedro hear the story, Claudio wants to die and to be with his wronged Hero. Leonato allows the two sorrowful men to continue to think Hero dead. In fact, they all attend her funeral. Leonato says that he will be avenged if Claudio will marry his niece, a girl who much resembles Hero. Although Claudio still loves the dead Hero, he agrees to marry the other girl so that Leonato should have his wish.
When Don Pedro and Claudio arrive at Leonato’s house for the ceremony, all the women are masked. Leonato brings one young woman forward. After Claudio promises to be her husband, she unmasks. She is, of course, Hero. At first, Claudio cannot believe his senses, but after he is convinced of the truth he takes her to the church immediately. Then, Benedick and Beatrice declare their true love for each other, and they, too, leave for the church after a dance in celebration of the double nuptials to be performed. Best of all, word comes that Don John had been captured and is being brought back to Messina to face his brother, Don Pedro, the next day. On this day, however, all is joy and happiness.