A carpenter John and his well liked wife Alison make extra money by renting out rooms in their home. They rent out a room to two students who both have a liking towards Alison, one of them being Nicholas.
Nicholas and Alisoun have been having an affair, and Absolon wants to create a courtship with her, all while she's still married.
Alisoun's scared that she'll get caught up in her affair, so she's extra careful about it and won't spend the entire night with Nicholas. And because she's busy with that, she ignore's Absolon.
John gets stuck in the bathtub in the other room, giving Alisoun and Nicholas time to be together. This is happening just as Absolon decides to give Alisoun a visit.
Absolon shows up at her window for a kiss but doesn't get one. Instead he's faced with the view of Alisoun and Nicholas together. Angry, he branded Nicholas. Nicholas cried out and John heard him, making him fall out the tub.
Alisoun and Nicholas convince the townspeople that John has gone mad before he could even tell them about Alisoun's affair.