Nicholas is the second character the narrator introduces. We learn that he is a poor scholar who boards with John.
Nicholas gets the action of the tale started when he sets his sights on Alisoun and successfully seduces her.
Nicholas conspires to trick John so that he can have an uninterrupted night in bed with Alisoun.
He spends all weekend in his room, and when a worried John sends a servant to check on him, he pretends to be in a supernatural trance.
When John questions him, Nicholas tells him that he's had a vision of a huge flood. John should prepare for it, Nicholas says, by hanging tubs stocked with food from the rafters and spending the night in one, so that when the flood comes, he can just cut the rope and float away.
While John sleeps in his tub, Nicholas has sex with Alisoun in John's bed.
When Absolon, angered at being tricked into kissing Alisoun's butt, returns to the window bent on revenge, Nicholas tries to get in on the joke by sticking his buttocks out the window. Instead, he gets branded by Absolon's hot poker.
In terrible pain, Nicholas cries out for water to douse the heat.
When John goes crashing to the floor, Nicholas runs into the street shouting in a panic.
When the townspeople gather at the scene, Nicholas helps Alisoun convince them that John is a crazy idiot.