After solving their last mystery at Spooky Island, the Mystery Inc. gang is back in Coolsville, where they are being honored with their very own exhibit at the Coolsonian Criminology Museum. However, when a masked villain steals costumes of classic monsters on display and brings them to life, the gang must come out of retirement to solve the case.
Thanks to his police officer father's efforts, Shawn Spencer spent his childhood developing a keen eye for detail (and a lasting dislike of his dad). Years later, Shawn's frequent tips to the police lead to him being falsely accused of a crime he solved.
Now, Shawn has no choice but to use his abilities to perpetuate his cover story: psychic crime-solving powers, all the while dragging his best friend, his dad, and the police along for the ride.