This Movie I watched as a kid around the late 70s to early eighties the plot as far as I remember was people living or visiting a house or hotel are being murdered, there is a teenage girl living in the house not sure if it was her’s but the scenes I recall are she and a young guy in a boat on a lake he makes advances on her and she freaks out. Also a scene where she is crawling in secret passages located in the house to the rooms where the victims slept. At the end of the movie it is revealed that she was born a Boy and was masquerading as a Girl the whole time. I remember it scared the hell out of me as a kid I think it was in color maybe made in the 70s period. Love know the title if anyone can help.