In Batman: The Killing Joke, after a series of events, Batman decides to go to the asylum of Arkham to speak with the Joker. Try to convince him that it is not necessary to kill each other, but it does not take long to realize that the one in the asylum is not the real Joker.
This, as always has the opportunity, has planned a way to take revenge on Batman and his friend Commissioner Gordon, a way that will hurt both, especially the commissioner, who will end up almost crazy.
Batman goes in search of the Joker very angry, but it has made a promise to Gordon, that is that it will stop the Joker according to the law, without revenge, a complicated promise to fulfill.
In the end the two characters meet and what happens is something about which the lovers of the comic, from which this work derives, have been talking and analyzing for years without agreeing.