The events of this story take place after the episode "Lesson Zero"

After the disaster that was the "want it need it spell" on Twilight's old doll Smarty Pants. It ended up in the care of Big Macintosh who has been seemingly possessed by the rag doll and acts like a foal. To make matters worse he is fine with how things are and wants to remain in diapers. But Applejack isn't going to let a rag doll possess her brother and will do everything she can to snap him out of the enchantment.