This was the third time that Kim Richards and Ike Eisenmann played a brother and a sister in a film. The previous two films were Escape to Witch Mountain (1975) and Return from Witch Mountain (1978), a theatrically-released film series from Walt Disney Productions.
The film was inspired by "The Devil's Platform", the seventh episode (of 20 total) of the horror TV series Kolchak: The Night Stalker (1974); however, the film's producers could not get permission to continue the storyline from the TV episode, so they opted to do a new one. Also, Tom Skerritt was in talks with Ridley Scott to do the film Alien (1979) and was unavailable for this film, so its producers offered the role of Mike Barry to Richard Crenna.