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.

加杰特是一名糊涂的探员，他的上司探长更是胆小得总是躲在自认为安全的地方发布命令。然而这么一对组合，竟然能时常挫败邪恶的Claw博士领导的M.A.D.军的阴谋。 这一切都归功于加杰特的侄女Penny和她的小狗暗中帮忙，以及他的经常歪打正着…