Invasion of the costumers!
Mabel and Dipper return to Oregon, but this time get to visit the city of Roseland! There they discover even the city has its own weird fauna...
There are people in Roseland who absently wander around in silly costumes who do crazy, weird things that no one can quite explain. Are they possessed? Is it a curse? Whatever it is, once they put on one of these costumes, they become obsessed with wearing it and staying in character! And it looks like Dipper got himself trapped! If Mabel and Suzie are going to help him, they need to get away to make a plan.
It would be easier to spot them if it weren't commonplace for people to run around in costumes who aren't under the influence of this dark(?) magic.