
This woman, who's name we learn is Ada, is to be married to a man that she has never met before. When this man comes to get her he leaves the piano behind on the beach because it was too heavy to carry back and he didn't want to use his men for that when they could get other things. Ada is pissed. She never really shows any love to her husband and soon seeks out another man, a man that is intertwined in the world of the local natives. He takes her to the beach and she plays a beautiful, even sensual, song, and the man is awestruck. He buys the piano from her husband in exchange for some land and a promise of piano lessons. It is with these piano lessons that his infatuation with Ada forms into a carnal desire for sex.
While Ada plays the piano the man who bought it, Baines, watches with admiration. Eventually he becomes desperate for a connection with Ada and tells her that, in exchange for a lesson per black key, she could have the piano back. After a number of lessons Baines starts "selling" black keys for sexual things, and eventually gets her to have sex with him. When Ada gets the piano back she becomes sad because she can't see Baines anymore, so she goes to him, unaware that her husband is following her.
When watching this film, at first, I thought that Baines was raping Ada, that he was a creepy dude who just wanted his desires fulfilled. About halfway through the film though I decided that it was not this way. This man became infatuated with Ada through her music and passion she puts into it. Instead of taking what he wanted he decided to barter with her. He fell in love and had to have some form of affection from her, and sex was what he decided on. Ada was as much a part of this transaction as he was, she gave him her body, and eventually wanted him when she got her piano back. So no I don't think this was rape, prostitution maybe, but not rape. I am also not saying that what he did was right, however.