For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Don Pedro's army arrives at Leonato's estate in Messina, where Claudio immediately falls in love with Hero. While Benedick and Beatrice once again engage in their long-running war of wits, Don Pedro wins Hero's love (and promise of marriage) in Claudio's name.
Act II
The cast attempts to trick Beatrice and Benedick into falling in love. Don John sets up a rendezvous with Borachio and Margaret (dressed in Hero's clothing), so that Claudio and Don Pedro "witness" Hero's unchaste, proposal-breaking behavior. Soon after, Dogberry and Verges arrest Borachio and Conrad after listening to the two recount Don John's evil plan. The wedding goes as Don John planned, however; Claudio leaves Hero at the alter after denouncing her.
Act III
Convinced of Hero's innocence, the Friar proposes a plan: start a rumor that Hero has died, in hopes that Claudio will remember his love for her. Beatrice and Benedick admit their mutual adoration. Dogberry and Verges bring Don John's evil scheme to light, and Don John flees. Ashamed of his misguided denouncement of Hero, Claudio agrees to marry Leonato's "niece" since Hero is "dead." At the wedding, the masked niece reveals her true identity, Hero; Beatrice and Benedick agree to marry; everyone is happy.