When Sarah is forced to babysit her half-brother Toby, she inadvertently summons the Goblin King and he whisks Toby away to his castle at the centre of a labyrinth. Sarah enters into a bargain with the Goblin King where she is given just thirteen hours to solve the labyrinth and rescue Toby, or else lose him forever.

Scooby-Doo and Shaggy must go into the underworld ruled by The Goblin King in order to stop a mortal named The Amazing Krudsky who wants power and is a threat to their pals: Fred, Velma, and Daphne.

Underlying disorder in Jared and Amy's relationship comes to a head when Jared becomes monomaniacally obsessed with going Goblin Mode.