With Coco and kitty in prison, Mystery Inc. thinks that they can finally enjoy a break.

Mystery Inc. has cracked the case to top all cases. They've tracked down Coco Diablo, the head of a notorious costume crime syndicate. Suddenly, menacing doppelgänger ghosts of the Scooby crew and favorite classic foes show up in Coolsville to threaten Halloween. Now it's up to the meddling kids to unmask the latest scoundrel and save Halloween.