It's Nightmare Night once again, and once again things are gonna go wrong. It seems that the Headless Horse, long thought to be an old pony's tale, is real, and is ruining Ponyville's Nightmare Night celebration! So Twilight Sparkle and Pinkie Pie, conveniently already dressed as Sherlock Pones and Dr Watson respectively, must work, with help from their friends, to solve the MMMystery of the Headless Horse. Can they do it before somepony looses their head to the phantom?