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
We are introduced to John, his wife Alisoun, and their boarder Nicholas. Nicholas and Alisoun begin to have an affair, and Alisoun catches the eye of the parish clerk Absolon.
Act II
Nicholas and Alisoun trick John into spending the night in a tub hanging from his rafters, so they can spend the whole night in bed together. Absolon appears at Alisoun's window in search of a kiss. Instead he gets a mouthful of Alisoun's buttocks.
Act III
Absolon, trying to get revenge on Alisoun, brands Nicholas with a hot poker. Nicholas's cry of "Water!" sends John crashing to the ground, and in the ensuing gathering of townspeople, Nicholas and Alisoun convince them that John is crazy.