Mystery Inc. has cracked the case to top all cases! They've tracked down Coco Diablo, the head of the notorious costume crime syndicate that colludes The Black Knight, Space Kook, and the Ghost Diver. With Coco and her kitty in prison, Mystery Inc. thinks that they can finally enjoy a break. Wrong! Suddenly, menacing doppelganger ghosts of the Scooby crew and favorite classic foes show up in Coolsville to threaten Halloween. Now it's up to the meddling kids — and their unlikely new partner Coco — to unmask the latest scoundrel and save Halloween! For Shaggy and Scooby-Doo, with trick-or-treating on the line — this time it's personal!