Case History: The gang are traveling to Franken Castle, an authentic Transylvanian castle brought over stone by stone from Europe. Before reaching it, they stop at a gypsy wagon to get their fortune told; she tells them that the castle caretaker has just been frightened off and warns them to stay as far as possible from the castle.

They dismiss her warnings and press on to the castle, where they are warned off at the drawbridge by a vampire. The others get off the drawbridge before it can rise, but Daphne is trapped inside the castle, where she is chased by a Frankenstein's monster. Shaggy and Scooby swing across to the castle to open the drawbridge; after lowering it, they are chased by a werewolf.

Fred and Velma find themselves in a dining hall; the vampire appears again, transforming into a bat and swooping down on them. Velma loses here glasses and, while crawling about looking for them, disappears through a trapdoor behind the fireplace. Meanwhile, Scooby and Shaggy have found the kitchen—and the Frankenstein monster. They land in the torture chamber, into which Velma has also blindly wandered. They find Daphne in a dungeon, rescue her, and trap the vampire. The four of them leave but get separated. Daphne and Velma hook up again with Freddy and look over a clue that Daphne has found: an inscription that seems to point to a treasure hidden in the Franken crypt.

Scooby and Shaggy, meanwhile, find and play around in a mad scientist's lab, narrowly avoiding both the werewolf and the Frankenstein's monster. They are discovered by the other three and together the five go down to the tomb, where they find the vampire resting in one of the crypts. It chases them; Shaggy and Scooby try to catch it with a tapestry, but it leaps back into the crypt, taking the tapestry with it. When they reopen the crypt, they find the vampire has disappeared, but it has left behind a gold earring, a ruby and a pearl. The ruby and pearl apparently have come off the tapestry (into which they had been woven); the gold earring is identical to one worn by the gypsy they saw earlier. Returning to the gypsy wagon, they find that "she" is actually a he: "Big Bob" Oakley (alias "The Actor"), who had been trying to scare people off so he could search for the Franken treasure.