While this film was based on
Ethel Lina White's 1933 novel "Some Must Watch," there are several major differences. In the novel, the maid stalked by the killer was crippled, not mute. It was also set in contemporary England, not early 1900's New England. Finally, the title of the film and the idea of incorporating a "spiral staircase" as a thematic element comes from another source entirely:
Mary Roberts Rinehart's 1908 novel "The Circular Staircase."
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