Matthew Lillard in a cave making a your momma joke

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.

An incredibly gullible college student can't seem to enjoy his own birthday party due to all of his friends making childish puns at his expense. The tension comes to a boil when somebody makes a "your mom" joke about his missing mother.