Alex is the English teacher of Michelle, the mistress of the rich businessman Henry. In the beginning she scorns their relationship believing that it is based on money and is demeaning to women but nonetheless she gradually forms a friendship with Michelle. As her sexual imagination begins to grow she falls under the allure of Henry and after she is seduced, she takes Michelle's place and becomes his mistress. The second half of the movie charts her downfall in the role of the mistress.
Some mild nudity but not in the sex scenes.
Alex imagines climbing on top of Henry and having sex with him while he is driving the car (49:54). Henry drops her off at her place, where her boyfriend is watching a game along with his buddies. Henry calls her on the phone and tells her to come back down because she forgot something. She throws the garbage as an excuse to get out and when she's outside, Henry kisses her. This starts their affair.
Alex and her boyfriend go to the cinema to watch a movie. Henry and his mistress happen to be inside the cinema too. When Alex comes to the bathroom, Henry follows her and they have sex inside one of the cubicles (56:26).
Alex and Henry have sex on a desk, share a bathtub (some mild nudity here), and kiss and frolic in the pool (56:26).