College freshman Elizabeth Ericson is thrilled to arrive with her best friend, Janet Shaw, at Midwestern University, her parents' alma mater. Liz and Janet hope to be accepted to the Tri-U Sorority, to which Liz's mother belonged. In fact, Liz feels that sorority membership is almost more important than her education, and is surprised when her and Janet's new roommate, Adelaide Swanson, expresses no interest in joining. During "Rush Week," Liz and her friends attend the social functions at all of the sororities, although Liz still has her hopes pinned on Tri-U, which is the most exclusive sorority. In addition to Tri-U sisters Marge Colby, Merry Coombs, Dallas Pruitt and Casey Krause, Liz meets Joe Blake, an older student going to school on the G.I. Bill. Liz likes the handsome senior, but refuses to listen to his condemnation of sororities as snobbish cliques. After Rush Week, the Tri-U sisters vote on the new pledges, and Liz is accepted, although Janet is not. Arrogant Dallas insists that Ruth Gates, a painfully shy girl whose mother was a Tri-U, be blackballed, but Casey pleads her case and Ruth is admitted. Despite Liz and Janet's girlhood pledge never to be separated, Liz reluctantly moves into the Tri-U house, while Janet, crushed at her rejection, leaves college and returns home. Liz is guilt-stricken over Janet's departure, but Joe assures her that time to mature may be just what Janet needs. As the weeks pass, Dallas attempts to "improve" the awkward Ruth, while Liz takes a liking to Chad Carnes, the most popular fraternity boy on campus, despite his reputation as a drunken womanizer. Hoping to impress the girls at the upcoming Christmas dance, Ruth goes into debt to buy an expensive gown. When midterm exams approach, Liz is frustrated by the noise at the Tri-U house and goes to the quiet dormitory to study with Adelaide. Liz is surprised to receive a call from Chad, who, in a panic, left his French exam without answering the questions. Chad begs Liz to complete the test for him, as he still has the questions, and he will then exchange her completed blue book for his blank one. Uneasy about cheating, Liz nonetheless helps Chad, who succeeds in switching the blue books and passes the exam. The sorority and fraternity members acclaim Liz as a hero, but Joe is disappointed by her lack of ethics and the two quarrel. Liz then gladly accepts Chad's pin, and that night, Chad and the other Lambda fraternity boys serenade her. Soon after, "Hell Week" begins, and the Tri-U sisters give the pledges humiliating and exhausting tasks to perform. One night, as the sisters concoct the next day's tasks, Dallas states that it is useless to assign anything to Ruth, as she will never vote to accept the still shy girl as a permanent member. The other girls agree that Ruth should be released immediately, and when Merry breaks the news to Ruth, she is crushed. Meanwhile, Liz is ordered to go to a neighboring town on a silly errand, but when Joe sees her at the bus stop, he invites her to a party. Weary of the nonsensical pranks, Liz goes and has a marvelous time with her non-sorority friends, whom she has not seen in weeks. A drunken Chad arrives, and when he chastises Liz for ignoring her duties, he and Joe get into a fistfight. Chad is ejected from the party, and Liz, who realizes that Joe is the better man, removes Chad's pin. When Liz returns to the Tri-U house, she learns that Ruth is missing. Disgusted to learn that Ruth has been "de-pledged," Liz runs through town looking for her, finally finding her in a feverish state attempting to complete her task. Ruth is rushed to the hospital, where she is diagnosed with pneumonia. Ashamed of her Tri-U sisters, Liz returns her sorority pin, which prompts Dallas and house mother Clark to suggest that Ruth be re-pledged in a special ceremony. Liz castigates them for their hypocrisy and snobbishness, then leaves with Joe. Outside, Liz wonders how her mother will react to the news, and Joe gently tells her that even mothers need to grow up, too.