A brainy school girl falls apart over a new, handsome teacher.

In 1946, as Margie and her teenaged-daughter Joyce are rummaging through an attic looking for an old dress, Margie finds an old pair of her bloomers in a trunk. Joyce asks her mother about her school days and, while an old Rudy Vallee recording of "My Time Is Your Time" plays on a wind-up phonograph which Joyce has found, Margie relates the story of her teenage years in the late 1920s: After pretty Marybelle Tenor finishes the same song in front of Central High School, Marybelle's boyfriend Johnny, replete with raccoon coat, comes to drive her home. Margie lives next door to Marybelle with her maternal grandmother, Mrs. McSweeney, and Marybelle and Johnny normally give her a ride home. This time, however, Margie who has a crush on Johnny, discovers that the elastic in her bloomers has broken and, attempting to repair the damage with safety pins, slips into the school's library. The librarian, Isabel Palmer, is visited by the handsome, young, new French teacher, Ralph Fontayne, who discovers Margie in mid-repair. Later, while walking home with Roy Hornsdale, who is smitten by her, Margie spots her father, Angus McDuff, driving by. Margie reveals to Roy that her mother died when she was a baby and her busy father lives apart from her. Invited to meet Margie's grandmother, Roy discovers that she has been a suffragette in the campaign for woman's right to vote and has raised Margie to take a deep interest in politics. While Margie is silently rehearsing her speech for an upcoming school debate on the topic of "Should We Take the Marines out of Nicaragua?", she is interrupted by Cynthia, the maid, and Margie stops to tell her about the new French teacher about whom all the girls are crazy. The next day, in the school cafeteria, Mr. Fontayne congratulates Margie on a theme she has written and promises to attend the debate. Marybelle is jealous of this attention paid to Margie and also of Mr. Fontayne's interest in Miss Palmer. The day of the debate, on snow covered streets, Roy arrives in his father's car to escort Margie. They stop at her mortician father's business where she leaves a message for him about the debate. Fortunately, he, her grandmother and Mr. Fontayne are able to attend and hear her deliver an impassioned argument to share America's freedom and to remove the U.S. Marines from Nicaragua. After the debate, everyone goes ice skating and while skating with Johnny, Margie's bloomers descend once again, causing her to fall. The chivalrous Mr. Fontayne, who is among those who run to help her, surreptitiously conceals and removes the garment, causing Margie some puzzlement as to just what happened to her bloomers. At home, where Margie is resting her sprained ankle, her father is still preoccupied by the issue raised in the debate. Mr. Fontayne comes to visit the "invalid" and discreetly hands her a present, the "handkerchief" she has lost. Some time later, Roy, who was supposed to be Margie's escort to the senior dance, comes down with a bad cold. When Marybelle taunts Margie by showing her orchids Johnny has sent her, Margie retaliates by inventing a mystery escort for herself. Meanwhile, Margie's father, after dismissing a salesman attempting to sell him candles manufactured in Nicaragua, phones Mrs. McSweeney, who tells him about Margie's escort problem and advises him to help out. Grandma then tells the unhappy Margie that she will have an escort to the dance. Just then, Mr. Fontayne comes by to deliver a grade for a theme Margie has written and privately confesses to Mrs. McSweeney that although he is to escort Miss Palmer to the dance, he would much rather be taking Margie McDuff. When Margie comes downstairs, she thinks Mr. Fontayne is to be her surprise escort, but upon reading the card enclosed in the corsage intended for Miss Palmer, has her hopes dashed. After Fontayne leaves, Margie's father arrives and the heartbroken Margie is delighted that he is going to be her escort. At the dance, both Johnny and Mr. Fontayne dance with Margie, much to Marybelle's displeasure. During a fast-paced dance with Johnny, Margie's bloomers descend once more. She pretends to faint and both Mr. Fontayne and Johnny go to her aid. In the attic, as Margie and Joyce laugh about the incident, Joyce wants to know who finally got to take her home from the dance and Margie replies that it was Joyce's father. As Mr. Fontayne, now the principal of Central High, enters the attic and kisses his wife, he has brought the day's newspaper which features a story that Margie's father has been appointed Minister to Nicaragua by the U.S. Senate. Margie and Joyce then dance to an old recording of "Margie," as Joyce tries to teach her mother some modern dance steps.