After receiving his military discharge, singer Don Collins proceeds to the address of the pen pal who corresponded with him while he was overseas. Helen Tyler answers the door and is perplexed by Don's expression of gratitude until she realizes that her teenage sister Susie is the singer's mysterious correspondent. The Tylers invite Don to dinner, and at the table, he inadvertently offends Helen, a schoolteacher, when he criticizes all teachers. When Don speaks of the difficulty he has experienced finding a singing job, Susie decides to organize a fan club to launch Don's career. Enlisting the help of her neighbor and would-be boyfriend, Howard Barnes, Susie writes a stack of fan letters and asks her relatives from around the country to post them. When R. N. Swanson, the owner of the local radio station, receives a deluge of letters in praise of Don, he hires the singer to appear on a radio spot. Susie recruits her friends to attend the broadcast and cheer on Don, making his performance a hit. Susie's decision to devote her life to promoting Don's career upsets her family, and when collect calls and telegrams from Don's fans come pouring into the Tyler house, Helen accuses Don of exploiting her sister. When Helen goes to the radio station to confront Don, Don invites her to dinner and Susie uses the opportunity to snap a publicity photo. The picture of Don and Helen appears in the local paper, and when the school administration worries that popular music may be corrupting the students, Helen suggests establishing a nightclub for the teenagers and Don promises to perform there. When Susie's hard work helps Don win his own radio program, he invites the teenager and her friends to be his guest at his opening at the Tahitian Room nightclub. Mistaking Don's gratitude for love, Susie decides to cause Don to lose interest in her older sister by telling him that Helen is engaged. Thinking that Helen has been leading him on, Don does not invite her to attend his performance. As Susie readies for her big night at the Tahitian Room, Helen wonders while Don excluded her from the party. Unknown to Susie, Swanson, who dislikes "bobby soxers," has arranged for the maitre d' to forget the teenagers' reservations, and when they arrive at the club, they are denied admission. Thinking that Don has forgotten her, Susie despondently returns home and breaks Don's record. When Helen tries to console her sister, Susie lets it slip that she lied to Don about Helen's engagement. Helen then shows Susie a letter from Swanson, notifying her that Don will be unable to perform at the teen club because of contractual obligations. The concept of a club for teenagers intrigues Quinlan, a local businessman, who attends opening night with the thought of starting up clubs all over the country. Susie, ashamed to face her friends with the bad news, decides to stay home until her mother convinces her that it is her duty to go to the club. When Susie announces that Don and the other performers will not appear, the teens begin to stream out of the building. Just then, however, Don, alerted by Howard to Susie's problems, arrives and dedicates his first song to Susie. After Don convinces Susie that he is too old for her, he apologizes to Helen. Susie then turns to Howard, a "man her own age," and all ends happily when Quinlan decides to launch teen clubs throughout America.