In this movie, the character Stephen Terrill is depicted as an inventor. In the original book this film is based on, he was a horror actor from the silent film era, who had the ability to appear in different costumes and make-ups (similar to Lon Chaney). He later became unemployed when the sound film was invented, because it required him to speak, and he couldn't hide his lisp and squeaky voice anymore. This resulted in the audience laughing at him, which depressed Terrill so much that he resigned from acting. Subsequently, he isolated himself from the public and resided in his castle, until he reportedly took his own life. Since then, Terror Castle was reported to be haunted by Terrill's ghost.
This is an adaptation of the first book in the Three Investigators series but the second movie.
The film is loosely based on the book "The Three Investigators and the Secret of Terror Castle".
In this film, Axel Milberg is playing Jupiter's father. In 2017, Milberg became the narrator of the popular German audio series "Die drei Fragezeichen", which is based on the The Three Investigator books.
In the movie, Jupiter's deceased parents are mentioned and even make an appearance. In the source story, his parents are neither making an appearance nor are they mentioned.