In commmon with all the previous "Treehouse of Horror" episodes, the program is made up of three self-contained stories; "I Know What You Diddly-Iddly Did", "Desperately Xeeking Xena", and "Life's a Glitch, Then You Die". The first story is a parody of the 1997 movie I Know What You Did Last Summer. In the second story, Bart and Lisa Simpson become superheroes. The final story makes light of the Y2K bug, a serious source of concern at the time that the program was first shown.