Fifteen-year-old Penny Wood is helping her neighbor, Chuck Harris, build a glider at the home of Elmer Tuttle, the Woods's handyman. Mrs. Wood, meanwhile, is busily planning a party to welcome her younger brother, Mervyn Roberts, home from college. Mrs. Wood, who worries that her daughter is more interested in becoming a writer than in dating boys, buys Penny a new dress for the party. Mr. Harris harbors concerns about his son, who wishes to become a mechanical engineer rather than a lawyer like his father. When Mervyn arrives home, accompanied by his wordly roommate, Roger Van Vleck, Roger, who fancies himself a ladies' man, begins to flirt with Penny. Smitten with Roger, Penny wears her party dress to dinner that night. The next evening, while Roger serenades Penny, she broaches the topic of marriage, much to his chagrin. The next day, Julie Harris, Chuck's older sister and the object of Mervyn's affection, arrives home from college, and Roger transfers his attentions to her. When Elmer warns Chuck that Mr. Woods is planning a visit to the Tuttle house, Chuck, who is hiding his creation from his father, enlists Penny's help in moving the glider to a neighbor's vacant garage. As they slip the glider into the garage, Penny hears Roger singing to Julie. Planning to fly the glider over the lake the next day, Chuck gives Elmer fifteen dollars to rent a boat to tow the glider in case it lands in the lake. When Penny learns about the money, she begs Chuck to lend it to her so that she can buy a new dress for the party. Chuck initially refuses, but when Penny bursts into tears, he gives her the money. After sending Elmer to purchase the dress for her, Penny presents Roger with a love poem. That night, dressed in her new strapless red dress and wearing too much makeup, Penny descends the staircase. When Mrs. Wood sees her daughter, she is shocked, but consents to Penny's wishes to enter the party dressed in her new finery. Greeted by rude remarks and derisive comments about her appearance, Penny runs back to her mother, who advises that she remove her makeup and wear her new jacket over the dress. While the crowd is preoccupied with Penny's appearance, Elmer and Chuck pull the glider from the garage and are seen by Mr. Harris, who angrily berates his son. Dr. Wood intervenes, however, and suggests that they discuss the issue after the party. Determined to fly his glider at any cost, Chuck decides to test it that night. Back at the party, Penny overhears Julie and Roger laughing at her love poem. When Penny bursts into tears, Mervyn tries to comfort her and presents her with the corsage he bought for Julie. At the lake, Chuck successfully launches his glider, but when Elmer is unable to spot him in the night sky, he returns to the party, alarmed. Mr. Harris and Dr. Wood immediately rush to the lake to search for Chuck, and when Mervyn offers to drive Julie there, she walks out on Roger. Bereft of female companionship, Roger tries to make up with Penny, but she is too concerned about Chuck to respond to his overtures. Meanwhile, at the lake, Chuck, soaring overhead, sees the search party looking for him. Distracted by his father's calls, Chuck crashes into a tree and smashes his glider. Impressed by his son's perserverance and ingenuity, Mr. Harris offers to help him build a new glider. When Chuck returns to the Woods's house, Penny is so worried about him that she slaps him in anger, and he responds by kissing her.