Novel involving soul of a physically challenged person possessing his brother's body

Question

The characters involves a psychiatrist/doctor, a girl and her sister. I guess the story goes like this - The sister commits suicide by jumping off a building. The girl tries to find out what caused her sister to do something like that. She ends up meeting a psychiatrist who used to treat her sister.

The girl gets hypnotized by the doctor and he informs her that she has got a twin personality (and I guess he tells her what the other personality's name is). She did not believe that first. But next morning she finds the name written near her bed.

Towards the end, girl finds out that the doctor manipulates girls' minds during hypnotism. His soul then enters the girls' bodies and uses them for his pleasure. I remember something like - causing pain to the body will break the connection.

Finally it is revealed that it is not the doctor but his physically challenged brother who is doing all this. The doctor's body is occupied by the brother's soul most of the time. During his transition into a girl's body, the doctor is locked up somewhere. I think the girl found this out through a letter from the doctor.

Answer 1

I believe that the book is "Sibs" by F. Paul Wilson. (Summary from Amazon) After vowing never to return, Kara Wade is back in New York City. She's come to claim the body of her twin sister Kelly, and to find out how she died. No secret as to the cause of death―a nearly nude, twelve-story plunge from a room in the Plaza Hotel―but Kara is determined to learn what led to that plunge.

Enlisting the help of an old lover, now an NYPD detective, Kara delves into her sister's life. Startling and bizarre facts begin to surface. Instead of answers, Kara finds more questions. Who was the stranger Kelly became during the months prior to her death? What was behind the perverse, decadent lifestyle she came to embrace so passionately?

Kelly's psychiatrist hints at a terrible secret in her past. But Kara shares that past with her twin. Is the sinister influence that drove Kelly into her bizarre double life about to overtake Kara as well? Sibs is F. Paul Wilson's most daring, most erotic, most deeply terrifying novel.