Scream of the Demon Lover (1970)

A beautiful young woman travels to a remote estate to seek employment as a biochemist for Baron Janos Dalmar. She finds herself attracted to him, so immerses herself in her work to suppress her lusty desires. A rash of rather brutal murders occurs in the area and she soon discovers that the Baron is not what he seems. Not long thereafter, the Baron transforms into a demon, and the beautiful young woman becomes his very own love slave.