Some autobots are captured. The remaining Autobots team up with some rebels to free their friends, the rebels know all the weaknesses of their enemies machines. They merge with the Autobots to become Headmasters to free their friends.
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.