[Book] A smut novel I can't find the name of..

The books name was something like '..secret..'

I don't know the name of the author or the year it was published. It could be around the 80s or 70s.

The story was about a girl who moves into a mansion where the family involved is full of incest and sex and affairs.

The female protagonist has a bad leg that she's sensitive about. Once she moves in with this family she sees a man fucking a girl in the pool.

The protagonist goes on to fall in love with the young manly son figure of the family. He was called Thomas or Tom or something .

The father was presently fucking the masseuse. There was a step daughter who in a past incident was bathed and massaged by the step father. The father massages the step daughter with cream which she says smelled like nivea.

There was another character who was somewhat evil. Her name started with a v and was like a daughter figure. She was into bdsm stuff with some ship captain or something.

In the end the father guy dies of a heart attack while fucking the masseuse on some drug which makes your heart beat slower. The mansion gets left to thomas. He and the protagonist live happily ever after.

The first page in the book (not the cover it was inside) was a woman in the state of undressing as seen from the back, in the process of removing her t shirt over her head.