Novelist investigating the twenty-year old Haymarket Strangler case slowly comes to realize that he is the actual culprit.
The closest Karloff came to playing Jekyll and Hyde, and he is quite excellent. A surprisingly competent little film with notable streaks of misogyny and sado-masochism running through it. The real core is an indictment of both Victorian hypocrisy and the pat decisions of psychoanalysis. No one in the film, especially Dawson's police inspector (who is so dim he could give Lestrade a good race), Turner's psychobabble spouting assistant and Aubrey's idiot daughter, seems capable of believing Karloff is the murderer, even though he is clearly a raving lunatic. But he is a gentleman, and gentlemen don't do nasty things like strangle and slash to death women, do they?
And gas lighting is probably not a good idea for an asylum cell. Just saying.