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.
Libby Parsons, wrongly convicted for her husband Nick's murder, thinks he is still alive and wants to settle the score and find their son. As she has been tried for the crime, she cannot be re-prosecuted if she finds and kills Nick.
A former Russian mobster named Ruslan, who is now a crime novelist, returns home and discovers his daughter is marrying his arch nemesis. His past also comes back to haunt him when his family is threatened. Hungry for justice, Ruslan returns to the life he once knew...with a vengeance.
