Nude for Satan (1974)

While driving through the countryside late at night, Dr. Benson finds a crashed car with a young woman hanging out of it. The doctor puts the girl in his car and drives for help to the nearest house, which turns out to be a mysterious castle. He is greeted at the door by a woman who looks exactly like the woman from the car, and she invites them both to stay for the night. The doctor soon discovers that his host is not the only one in the castle, and that this beautiful woman is concealing a terrifying secret.