There is a legend in Ponyville about a room… Ponies believe that this place is where a serial killer lives. Of course that's fake, it's just a tale to set curious fillies straight. But in the back of every Colt and Mare's mind they know this room is true. And when mass murders take place they know the murderer is back, but who is the murderer. With the help of Twilight and the Gang they uncover who the killer is and they have to stop them at whatever cost.