Mystery Inc. has cracked the case to top all cases! They’ve tracked down Coco Diablo, the head of a notorious costume crime syndicate. With Coco and her kitty in prison, Mystery Inc. thinks that they can finally enjoy a break. Wrong! 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!

In a world of anthropomorphic animals, a reclusive wolf's complicated relationship with a kindly rabbit is tested by a classmate's murder, a charismatic deer's influence, and his own burgeoning predatory instincts.