Night Monster (1942)

Dr. Lynn Harper, psychologist, has been called out to the old Ingston Mansion, a dark and mysterious place with a very bad reputation, in order to make an assessment of the sanity of Margaret Ingston, daughter of patriarch Kurt Ingston. She claims to be sane, but she is clearly very disturbed; we can't be certain, although the doctor gives her a clean bill of health. But then Dick Baldwin shows up on the scene, just when Dr. Lynne has been receiving thinly veiled threats from the inhabitants of the house. He's our hero. Three medical doctors have been invited out to the mansion as well, Dr. Timmons, Dr. Phipps and the sleazy Dr. King (Lionel Atwill). One by one the doctors are mysteriously murdered. Dick Baldwin must figure out who is doing the killings, and he must do so before whoever it is can kill his new love interest, Dr. Lynne Harper. But the only one he can trust is Kurt Ingston himself, since Ingston has no legs and can't have perpetrated these murders. Is it sinister Rolf, the butler, or Laurie, the sex crazed and sociopathic chauffeur, or Agor Singh, the Hindu Yogi with his strange ways? And of course, Lynne might be wrong, Margaret may be very insane, and she might be the culprit.