The Dark Other

Stanley Weinbaum¿s The Dark Other was first written sometime in the 1920s under the name The Mad Brain. The manuscript went unpublished until 1950, where it was posthumously released with edits by Forrest J. Ackerman.
Patricia Lane is a spirited young woman, in the midst of a passionate relationship with Nicholas Devine, a writer with a fascination with horror. When he starts to show bizarre personality shifts, she turns to her neighbor, a talented psychologist, to discover the source of these outbursts.