A ghostly voice calls out from a spooky mansion, beckoning to a man walking in a trance. On their way to visit their friend Sharon Wetherby, the Mystery Inc. gang see this odd sight. When they arrive at the Wetherby's, they learn that Sharon's Uncle Stuart is missing, and they deduce that he was the man they saw going into the deserted Kingston mansion. Investigating, the gang find Uncle Stuart, but he has been transformed into an old man. He tells them that he was called out of the Wetherby house by the Ghost of Elias Kingston, who demanded that the Wetherby fortune be surrendered to him, otherwise he would put an old-age hex on the family; he turned Uncle Stuart into an old man as a warning. While Mr. Weatherby goes to speak to the sheriff, the gang stay behind with Sharon and her enfeeb