The Big Idea Behind THE SPIRAL STAIRCASE
David O. Selznick picked up the property as a potential project for his biggest contracted star, Ingrid Bergman.
Strapped for money he needed to complete his epic Western Duel in the Sun (1946), Selznick sold the rights to Some Must Watch and several others (including The Farmer's Daughter  and The Bachelor and the Bobby-Soxer ) to RKO. Under the terms of that agreement, Selznick got a cut of the movie's future earnings and furnished the services of producer Dore Schary.
Schary, who was an Academy Award®-winning screenwriter (Boys Town ) before moving to producing, brought in a first-time scripter, Mel Dinelli, to adapt the novel to the screen. At this point, it was known by its working titles "Some Must Watch" and "The Silence of Helen McCord."
During story conferences, Schary and Dinelli changed the setting to turn-of-the-century New England, which they thought would not only be more picturesque but would give it a more threatening gothic atmosphere. They still had to solve one issue that troubled them about the terrified heroine. "Why doesn't she just scream?" Schary asked, inspiring them to change the character from lame to mute.
According to some reports, Helen Hayes also had a hand in shaping the new character and setting due to her success in the radio play.
Looking at visual possibilities, particularly for the tense climax, Schary and Dinelli borrowed elements of the setting and title of Mary Roberts Rinehart's novel The Circular Staircase.
By the time Selznick sold the property, Ingrid Bergman had passed on it, so Schary cast another Selznick discovery, Dorothy McGuire. He also brought in Rhonda Fleming from the Selznick roster to play the secretary torn between the two half brothers in the story.
Siodmak was loaned to RKO for The Spiral Staircase. The German-born director had been working at Universal where he brought his country's characteristic Expressionist style to such thrillers as Phantom Lady (1944), The Suspect (1944), and The Strange Affair of Uncle Harry (1945). His skills in the genre made him a natural choice for this assignment.
Ethel Barrymore was in talks with RKO to star in a film of Frank Baker's supernatural novel Miss Hargreaves, but the project was shelved, leaving her available to accept the part of the invalid Mrs. Warren.
George Brent, a much sought-after leading man for a number of years, had just signed a lucrative two-picture deal with RKO. The Spiral Staircase became the first project under that contract.
by Rob Nixon