While Alfred C. Kinsey, a zoology professor at Indiana University, trains three assistants to interview people for a new study, their questions prompt him to recount his life: Throughout his childhood, Kinsey, his mother Sara, brother Robert and sister Mildred are dominated by his strict, bullying father, Alfred Seguine Kinsey. During his Sunday school lectures, the elder Kinsey, a devout Methodist and college professor, rails against any sort of immorality. As a boy Kinsey suffers from debilitating illnesses and it is not until a doctor prescribes walks in the woods that he recovers his health. Kinsey discovers a passionate love of biology on his hikes, which enable him to escape the stifling atmosphere at home. One day, the teenaged Kinsey, now an Eagle Scout, confesses to a friend that although he wants to study biology, his father has decreed that he become an engineer. Kinsey’s unhappiness is heightened by his sexual frustration, as his religious upbringing has made him feel ashamed of all sexual urges, including masturbation. Finally, unable to bear his father’s inflexible code of morality, Kinsey lashes out, announcing that he has quit the college at which his father teaches. Although his father pronounces him a disappointment, Kinsey thrives and becomes an assistant zoology professor at Indiana University, where over the years he amasses a huge collection of gall wasps and becomes a renowned entomologist. During one of his lectures, his enthusiasm for his subject piques the curiosity of student Clara “Mac” McMillen. Mac approaches the socially awkward Kinsey one afternoon, and later, as he fixes her a picnic, he shyly relates that his graduate students have nicknamed him “Prok,” an abbreviation of Professor Kinsey. Soon Kinsey falls in love with Mac, an intelligent “free-thinker” who enjoys nature and biology. Kinsey is crushed when Mac does not accept his marriage proposal, telling him that she finds him “too churchy,” but eventually Mac changes her mind and they are married. On their wedding night, the two virgins are so sexually unaware that their attempt to consummate their marriage is a dismal failure. The next evening, while they dine with Kinsey’s parents, Mac tries to defend her husband against his father’s belittling by revealing that his new biology textbook is used throughout the country. Later that night, Kinsey’s laughter over his father turns to tears, and Mac comforts him by telling him how much she loves him. Suddenly realizing that they can overcome their sexual difficulties by consulting an expert, Kinsey jumps out of bed and packs their suitcases. Soon after, a doctor explains that Mac’s thick hymen impeded their union, and after the problem is corrected, the couple enjoy an active, joyful sex life. Their first daughter, Anne, is born in 1923, and by the time their children Joan and Bruce are born, Kinsey and Mac have cemented their firm partnership. Kinsey becomes known throughout the university for offering advice about sex to married students, and one afternoon, is amazed by the ignorance of a couple who come to him for help. When Kinsey discusses the situation with Mac, he blames societal misconceptions about sex on the lack of scientific studies on the subject. That evening, the university’s new president, Herman Wells, hosts a party celebrating the publication of Kinsey’s new book about gall wasps and Kinsey grimly realizes from Herman’s inability to grasp the subject how overly specialized his work of twenty years has been. During the party, Kinsey upbraids his colleague, Dr. Thurman Rice, for the ineffectualness of his hygiene course and tells Herman that the university must offer a class on sexuality. Although Herman is cautious, after he attends one of Rice’s insipid lectures, he agrees to Kinsey’s suggestion. Soon Kinsey’s lecture hall is overflowing with students eager to take his “marriage course,” during which he offers basic biology instruction and frank information about sex. Especially impressed by Kinsey’s dynamic, nonjudgmental attitude is student Clyde Martin, who becomes Kinsey’s assistant. Kinsey asks his students to fill out questionaires in order to build statistical data about the sex lives of typical Americans, and Clyde, who is open about his past relationships with both men and women, suggests that people would be more willing to confide their secrets to him if he were to talk to them confidentially rather than ask them to commit their private lives to paper. Clyde’s suggestion inspires Kinsey to approach different groups in person, and one evening, after Clyde and Kinsey have visited a bar for homosexuals in Chicago as part of their study, Clyde asks Kinsey about his own feelings toward homosexuality. Kinsey admits that as he has gotten older, he realizes that he is bisexual, then responds passionately when Clyde kisses him. Kinsey, not wishing to keep anything from Mac, tells her of his affair with the younger man, and although Mac is hurt, she realizes that she has always been aware of Kinsey’s possible bisexuality. As their work progresses, Clyde becomes a member of the family as his affair with Kinsey continues until one day, he announces that he would like to sleep with Mac instead. Forced to prove his belief that sex does not have to involve love nor interfere with it, Kinsey accepts Mac’s new relationship with Clyde. In class, Kinsey continues to lecture that it is injurious to allow religious morality to dictate what is considered “normal.” In order to expand his studies, Kinsey seeks a grant from the Rockefeller Foundation, and despite the initial reluctance of administrator Alan Gregg, the grant is secured and Kinsey hires two scientists, Wardell Pomeroy and Paul Gebhard. Kinsey trains them and Clyde in how to take sexual histories using a specialized code that only they can decipher. Using a nonjudgmental, friendly approach, they spend several years amassing thousands of sex histories throughout the United States, and in 1948, Kinsey’s groundbreaking book, Sexual Behavior in the Human Male , is published. Kinsey is lauded for his enlightening work, although Alan cautions him when the scientist calls for the reformation of laws governing sex acts. Alan also expresses concern about Kinsey’s new studies into female sexuality, and Kinsey admits that he and his team have been using movie and still cameras to record sex acts. Unknown to Alan, Kinsey encourages his assistants and their wives to experiment with different partners, and Kinsey and Mac also participate in the movies recording sexual encounters. When the Rockefeller Foundation gives him another grant, Kinsey establishes the Institute for Sex Research at the university, but after his companion book about female sexuality is published, Kinsey is vilified by academics and the public. Baffled by the hypocrisy, Kinsey is further infuriated when U.S. Customs seizes a shipment of erotic images and artifacts that he has bought for the institute’s collection. As the government begins to investigate rumors that Kinsey is involved with Communists, he must battle the Customs department in an expensive court case. Desperate to distance the foundation from Kinsey, Alan discontinues his grant, while Herman is unable to obtain funding for Kinsey from the university’s board of trustees. Disillusioned and overworked, Kinsey suffers a heart attack. As Mac helps him recuperate, she continues to encourage him, although he laments that he cannot help the thousands of people who still write to him seeking advice. Kinsey and Mac travel to San Francisco to meet grocery store heir Huntington Hartford, but the eccentric millionaire refuses to fund Kinsey’s research for further volumes, declaring that it is too controversial. The next morning, Kinsey takes one last sex history before leaving, and the woman he interviews describes her despair upon realizing that she was attracted to another woman. After reading Kinsey’s book on female sexuality, however, she says, she realized that there were many women like her and consequently has been in a committed relationship with another woman for three years. When she thanks him for saving her life, Kinsey realizes how valuable his work has been. Kinsey and Mac then stop in a redwood forest on their way to the airport, and Kinsey, re-energized by the woman’s story, as well as by his love for nature and Mac, tells his wife that they have much work left to do.