The whole congregation is summoned in the church. Claudio and Hero stand in front of Friar Francis who opens the wedding ceremony and invites anyone knowing of any inward impediment to the marriage to speak forth. Claudio asks Hero if she knows of any, which she negates. Thereupon he bids Leonato to take his daughter, "this rotten orange", back, as he himself does not wish to be married to "an approved wanton". He accuses Hero of being innocent in appearance only, but in true nature lecherous. Leonato, being aghast, asks Don Pedro to intervene, but the prince joins the slandering instead, calling Hero "a common stale". Claudio wants Hero to tell the name of the man she was with the other night. As Hero denies having seen any man, Claudio states that Don Pedro, Don John and himself had witnessed her being unfaithful, and afterwards questioned Borachio, who affirmed that they had been meeting for a while now. Affronted with these heavy charges, Hero faints. Don Pedro, Claudio and Don John leave the church.
Hero lying on the ground as if dead, Leonato bursts forth that he indeed would prefer she were, given her shame, deploring the daughter he once was proud of. However, Beatrice immediately confirms that she believes Hero is not guilty, but rather the victim of an intrigue. Leonato does not agree and asks the others to "let her die". Hereupon Friar Francis takes the word and pleads for Hero's innocence, claiming that his age and life experience tell him so. He asks Hero, who has recovered, to talk about the man she was seen with, but she again denies that she had met anyone. Benedick suspects Don John to be the author of all the trouble, and Leonato vows to "tear" his own daughter if the accusation are true, but if not to avenge Hero. Friar Francis, however, brings forward another plan: he advises Leonato to bandy about Hero's death due to the shock following the slandering. While her official burial is held, Hero herself should stay hidden inside the house. As Claudio hears of his former bride's death and his own share in it, the friar hopes to move him to remorse and to test his love observing how earnestly he mourns. If the slanderer will not be moved, however, Hero could still spend the rest of her life in a nunnery where no one would know of her shame.
As Hero is lead away into the house, Benedick and Beatrice remain behind. She is overcome with indignation and wishes for a man to right her wronged cousin. Benedick reveals his love for Beatrice to her and asks her what he can do. Beatrice requites his declaration of love and tells him to kill Claudio, which Benedict instantly refuses, whereupon Beatrice turns to leave. Holding her back, Benedick wants to know whether she truly considers Claudio her enemy. Having heard her vehement affirmation, he swears to challenge his former friend and leaves.
Dogberry, Verges and a Sexton meet their captives Borachio and Conrade in prison for the questioning. The two offenders' names are taken down and the Sexton calls in the accusers, the watchmen. They point at Borachio and report how they overheard him and Conrade talking about their part in Don John's intrigue that lead to the slandering of the alledgedly unfaithful Hero. The Sexton tells them that the said Hero had died due to the public shaming and that Don John has fled from the city. Furthermore, he orders Borachio and Conrade to be brought before Leonato.