CARNAL KNOWLEDGE

In 1946, Sandy, a student at Amherst College, meets a Smith College student named Susan at an on-campus event and they begin dating. While they enjoy each other's company, Susan is hesitant to take their relationship to a physical level. Sandy shares the intimate details of their courtship with his roommate, Jonathan.

After Sandy reveals that he and Susan finally shared a fleeting moment of physical intimacy, a curious and competitive Jonathan decides to ask Susan out behind Sandy's back. Jonathan and Susan eventually sleep together. He tries to convince her to stop sleeping with Sandy, but despite her initial hesitation, Susan ultimately gives in to Sandy as well.

As Jonathan pressures Susan to break up with Sandy, she finds herself torn. Ultimately, she makes her choice, calling Jonathan to tell him that she is leaving him to commit fully to Sandy.

In 1961, Sandy is married to Susan, while Jonathan still searches for his "perfect woman". Jonathan begins a relationship with Bobbie, a beautiful but shallow woman, but he eventually grows bored with her. Bobbie leaves her job at Jonathan's suggestion. She then becomes depressed, spending long hours doing nothing but sleeping in the apartment she shares with Jonathan. The relationship deteriorates. Jonathan berates Bobbie for not cleaning up the apartment while he is out working all day at a nine-to-five job. He claims that he does not understand why break-ups always have to end with "poison".

Sandy's relationship with Susan is faring no better. Sandy is dissatisfied and bored with the physical part of their relationship, even though he and Susan "do all the right things". He relates how they are "patient with each other" and concludes with a statement that perhaps sex is not "meant to be enjoyable with the person you love".

Sandy begins dating Cindy. Sandy, Cindy, Jonathan, and Bobbie find themselves together at Jonathan's apartment, where Sandy complains privately to Jonathan about his sex life with Cindy. Jonathan suggests to Sandy that they trade partners, to "liven things up a bit". Sandy goes to the bedroom looking for Bobbie. Cindy dances with Jonathan and reprimands him for attempting to bed her with Sandy nearby, but indicates she is open to seeing him on his own, saying he should contact her at a more appropriate time. In the meantime, upset by an earlier fight with Jonathan about her desire to get married, Bobbie has attempted suicide. She is found by Sandy, who calls the hospital to have her taken to intensive care.

In 1970, Jonathan presents a slideshow entitled "Ballbusters on Parade" to Sandy and Sandy's 18-year-old girlfriend, Jennifer. The slideshow consists of pictures of Jonathan's various loves throughout his life. He skips awkwardly over a slide of Susan, but not before Sandy notices. He also shows an image of Bobbie, saying they are divorced and have one child together, and he is paying her alimony. Jennifer and Sandy leave wordlessly. Some time later, Jonathan and Sandy walk down Park Avenue and discuss their lives.

Jonathan solicits a prostitute named Louise, and they go through a ritual dialogue about male–female relationships which is apparently a script written by Jonathan. At the end, Louise recites a monologue (again scripted by Jonathan) praising his power and "perfection", which apparently has become the only way Jonathan can now get an erection.