Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
A carpenter named John lives with his much younger and very pretty wife Alisoun in the university town of Oxford. To make a bit of extra money, he boards a poor young scholar named Nicholas in the spare bedroom.
The description we get of John's domestic situation perfectly sets us up for the conflict that's to follow. We learn not only that Alisoun is much younger than John and very beautiful (from a medieval point of view, a clear indication that she's likely to cheat on him), but also that John boards a young man in the house. You can pretty much guess what's coming.
Conflict
Nicholas and Alisoun begin an affair, and Absolon courts Alisoun unsuccessfully.
Obviously, Alisoun's role as Nicholas's lover conflicts with her role as John's wife. And Absolon's courtship of Alisoun is unwelcome, since she already has both a lover and a husband. This second plot strand will be wound into the first with great effect at the conclusion.
Complication
Alisoun is afraid that John will catch her and Nicholas shacking up. She's extra-cautious about the affair, which means that Nicholas can't have Alisoun all to himself for an entire night. And Alisoun rejects Absolon's advances, since she's distracted by Nicholas.
These are the conflicts that drive the remainder of the plot. Alisoun's caution prompts Nicholas to trick John into believing he needs to sleep in a tub hanging from his rafters, thereby leaving Nicholas and Alisoun to frolic undisturbed. And Alisoun's repeated rejection of Absolon's seduction attempts only seems to spur him on.
Climax
John climbs into the tub hanging from the rafters, clearing the way for Nicholas and Alisoun to get it on. Meanwhile, Absolon learns that no one's seen John all day and makes plans to woo Alisoun later that evening.
This is the moment when the set-up comes to fruition and the complications are addressed. With John in the next room while Nicholas and Alisoun frolic and Absolon on his way to the house, it's the point at which the potential for conflict is at its highest.
Suspense
Absolon shows up at Alisoun's window in search of a kiss, but instead gets a mouthful of nether half.
Tensions are high: will John wise up to the trick and catch Nicholas and Alisoun in bed together? How will Nicholas handle Absolon's attentions to Alisoun? And how will Absolon react to his humiliation? Will John ever get out of that tub? This is the moment of suspense, the point at which many more questions are raised than answered.
Denouement
An angry Absolon brands Nicholas's butt with a hot poker, causing him to cry out for water. Hearing his cry, John cuts the rope attaching his tub to the rafters and takes a nasty fall.
Here we get answers to the questions we were wondering about in the suspense stage. John fails to wise up, Nicholas handles Absolon's attentions to Alisoun by continuing the joke she started, Absolon reacts badly to his humiliation, and John does get out of that tub, although painfully.
Conclusion
The bemused townspeople gather around a prostrate John and agree with Alisoun and Nicholas's assessment that he is crazy.
Final questions are tied up here. You may have been wondering if John will figure out he's been had once he sees Nicholas and Alisoun together and realizes there's no flood. If he does, we never get a chance to hear about it, because his protests are drowned out by Alisoun and Nicholas's insistence that he's crazy. Their success in convincing the neighbors of John's insanity rules out any possibility for John to make a case against Nicholas, for no one will believe anything he says from now on. The possibility of conflict averted, the story is over.