This movie was intended as a pilot for a TV series of the same name. It was not picked up by NBC; that's the reason for the ambiguous ending that leave the viewer hanging in mid-air.
The Cort estate/house is also the location of the where the vampire (Catherine) hides at the end of episode 4 of the TV series "Kolchak: The Night Stalker" (aired 10/04/1974) - a series that also started out as a Dan Curtis production.
Roy Thinnes would later star as Roger Collins/Reverend Trask in the 1991 revival of Dark Shadows which was produced by Dan Curtis.
When the publisher and his friend board the cable car the passengers facing the camera look at the camera. As it moves on, the passenger at the back rubbernecks at the camera.
Claude Akins and Stanley Adams previously played partners in crime in Incident of the Druid Curse (1960).