The Joker commits crimes in which bad jokes make people laugh uncontrollably, whereupon he robs them.
The Joker has returned and is committing robberies in which he tells a bad joke that surprisingly makes everyone burst out in a fit of laughter, then he robs everyone using a gimmick based on the joke which he tells. When Batman and Robin attempt to stop him they too find themselves caught in a fit of uncontrollable laughter.
Returning to the Batcave, they find that the Joker sprayed them with a form of "loco weed" that made them hysteric. Devising an antidote to prevent it from happening again, their next attempt to stop the Joker is foiled when the Joker deduces this idea and uses a spray that causes the dynamic duo to burst out in tears instead.
Chasing the Joker again, they manage to catch him in front of a police house, but when they try to lock him in one of the cells in it, the Joker sets off his trap causing the cell door to flip around and lock Batman and Robin in, the Joker then flaunts the key in front of them and informs the caped crusaders that he is about to steal an experimental new satellite that is to be launched into space.
Caving a key out of the leg of a footstool in the cell using his photographic memory, Batman gets them out of the cell and they confront the Joker, beating him this time and lock him up, and leaving him to endure the mocking laughter of his fellow inmates.