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.
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.
According to actor Ike Eisenmann, neither he nor Kim Richards was aware eachother had been cast in the film. They met eachother on set and laughed when they realized they would be playing brother and sister, as they had previously famously played siblings Tony and Tia in Escape to Witch Mountain and its sequel Return from Witch Mountain. They asked the production team if they were aware of this previous connection, and were told their mutual casting was a complete coincidence.