This was an adaptation of a Broadway play called "Without Warning". It opened at the National Theatre in New York on May 1, 1937 and ran for 17 performances. Eddie Craven originated his movie role in the play.
According to a contemporary article in Film Daily, Jane Wyman was originally cast in the role of "Sally".
For some unknown reason, Karloff is made up to look like his frequent co-star, Edward Van Sloan, with brushed back white hair and thick glasses.