At the Harrad college orientation meeting at the beginning of the new term, the director of the school, Dr. Philip Tenhausen, welcomes the new students and introduces his wife, Margaret. He explains that the Harrad experiment is one of self-exploration through pre-marital relations and that the students have been matched with roommates with whom they are encouraged to share sexual intimacy and remain as a couple for one month. When new student, Harry Schacht nervously enters his room he finds his self-assured roommate Beth Hillyer naked in the bathroom. Steeling himself, Harry goes in to talk to Beth, who wonders if Dr. Tanhausen expects them to sleep together the first night and smiles when he nervously musters, “I doubt it.” Meanwhile, cocky young Stanley Cole drives to a roadside café called Jack’s Place to ask directions to the campus. When Jack and a patron at the café snicker, asking if he’s studying “biology,” Stanley is unfazed by their ridicule and leaves. Back in the dormitory, Harry smokes a cigar to impress Beth and says he is relieved to not be matched with a girl who looks like him. In response, Beth tells him to stop the self-criticism, put out the cigar and be himself. Finally arriving at school, Stanley enters his room and his roommate Sheila Grove shyly introduces herself. She pretends not to notice when he casually undresses to shower or when he returns naked and goes to bed. The next day, as Sheila and Stanley walk with plump, verbose Wilson and his friendly roommate Barbara, Wilson frets over the rule that all exercises be done in the nude, while Stanley flirts with Barbara. Then in the yoga class, Harry notices Stanley flirting with Beth, as the naked boys and girls sit in a circle holding hands, saying “zoom” to the person next to them and going around faster and faster. Back in their room, Stanley plants seeds in a window box and instructs Sheila on how to nurture tiny plants. He tries to kiss her, but she asks if they can wait since they are strangers. Later, Harry and Beth sit under the trees talking and when he tickles her, they fall onto the grass laughing and kissing. While Wilson is out jogging, Stanley enters his room and when he returns early to find Barbara naked with Stanley, he punches him in the nose. Walking across campus together, Harry and Stanley discuss Sheila and Harrad, which Stanley bitterly calls an experimental lab. When he later moves their beds together, Sheila is so uninterested that he angrily leaves. Proceeding to the pool, Stanley swims naked and alone until Sheila joins him. Saying that she is trying, Sheila drops her robe and swims to him. The pool soon fills with students, including Barbara and Wilson, who get cheers when he bravely drops his towel. Walking back from the pool with a group, Stanley cynically questions Dr. Tenhausen’s true interest in the experiment and wonders if the one month rule applies to Margaret. When Barbara presses him about his relationship with Sheila he admits that she is still a virgin. Back in their room, he and Sheila argue about her reluctance to sleep with him, with her asserting she does not want to make a mistake and him retorting she is making one by abstaining. That weekend, after having sex with Stanley, Beth tells Harry about the encounter, but Stanley decides to not tell Sheila. Later, Stanley and Sheila go to Jack’s Place, where they are watched by a heavy-set man in a cape at another table. When Stanley goes to the restroom the man sits down with Sheila, introducing himself as Sidney Bower and making suggestive remarks to her and about Harrad. She is defending the school and asking him to leave before her friend comes back, when Stanley returns and offers to sell her for fifty dollars and Bower’s cape. Stanley even leads Sheila outside with Bower following, but he whispers to her “Trust me.” As Bower is leading her away, Stanley mentions she has left her purse in his car and when she goes to get it, they drive away. That night Sheila thanks Stanley and asks if they can make love, assuring him that she is ready. They then lie on the bed, kiss and turn out the light. The next day they study under the trees as a happy couple, enthusiastically working on a paper together. Nearby, Harry is upset because Beth has just told him about sleeping with Stanley. Sheila interrupts their conversation to invite them to a picnic with her and Stanley, happily telling them that the weekend was their turning point. This confuses Harry, who assumes she is referring to Stanley’s encounter with Beth. Once on the picnic, Sheila talks enthusiastically about Harrad and Harry commends her lack of jealousy over Stanley’s infidelity. The news shocks Sheila who angrily mocks Stanley for his pretense of patience with her and runs off. When he finds her in the greenhouse and apologizes, she accuses him of having no feelings and he replies that he has not felt anything for a long time. Later at Dr. Tenhausen’s lecture on group marriage, Wilson asks why he and Margaret advocate non-traditional values when they are monogamous. This prompts Stanley to take a hard look at Margaret who looks back quizzically. When the group leaves, Dr. Tenhausen praises Stanley and Sheila for their paper and asks if they will play badminton with him and Margaret and although they are barely speaking, they agree. The four play badminton and during a break, Stanley suggests switching partners, pairing himself with Margaret. After the game, Stanley sees Margaret and Sheila walking across campus together. When Sheila leaves he joins Margaret and makes small talk until she asks what he really wants from her. She accuses him of wanting to add her to his list of conquests and surprises him by suggesting they have sex then and there. Choosing a highly visible place in front of the school, she undresses to her underwear and Stanley, realizing she is calling his bluff, walks away embarrassed. The Tenhausens discuss the confrontation, wondering why Stanley is rebelling against them and the project and Dr. Tenhausen decides to talk to him. When he finds Stanley about to leave, he states he will not expel him, so he cannot use them as an excuse to run away, but Stanley walks past him and off campus. As Sheila sits by Stanley’s seedlings, reading a note and looking sadly out the window, Stanley drinks coffee at Jack’s. When Jack asks him if he thinks she will come, he replies that he does. Then when Stanley finally gets up to leave, Jack says, “You’ve got it whipped. No ties, no promises, you don’t belong to nothing…really terrific.” Stanley replies, “Yeah, terrific” and leaves. Back on campus, Stanley discovers his room empty and goes to Harry and Beth’s room where he finds Sheila. After he says that he thought he had someplace to go, but has decided to stay, Sheila smiles and offers her hand. The four of them then hold hands in a circle and say “zoom” around it once, embrace each other and laugh.