High Quality Content by WIKIPEDIA articles! "Treehouse of Horror XX" is the fourth episode of The Simpsons` twenty-first season. The episode first aired on October 18, 2009 on Fox. This is the twentieth "Treehouse of Horror" installment, containing three self-contained stories: In "Dial `M` for Murder or Press `#` to Return to Main Menu," Lisa is forced into a Hitchcockian murder scheme by Bart; in "Don`t Have a Cow, Mankind," Springfield is once again overrun by zombies thanks to Krusty Burger`s latest sandwich; and in the Sweeney Todd parody, "There`s No Business Like Moe Business," Moe the bartender bleeds Homer dry to create the perfect microbrewed beer. An estimated 8.59 million viewers tuned in to watch the episode. This is the first Treehouse of Horror episode to air in HD.