Wealthy playboy Kenneth Marquis is divorcing his third wife, and seventeen-year-old Corliss Archer, whose father Harry is the attorney for Mrs. Marquis, follows the trial avidly. After the matter has been decided, Marquis and his lawyer, Taylor, come to Harry's office to discuss Mrs. Marquis' huge settlement, and as soon as Corliss meets Marquis, she is smitten by the suave older man. Marquis plays up to Corliss, enjoying her father's irritation. The next day, Harry tells Corliss that he saw her boyfriend, Dexter Franklin, with another girl at the Penguin Club, a local restaurant notorious for its back-room gambling. That night, while Corliss and her friend, Mildred Pringle, are having a slumber party, Mildred's enterprising younger brother Raymond comes over and offers to bind Corliss' diary in leather for a fee. Corliss instructs Raymond to come back tomorrow, then tells Mildred that she will get even with Dexter by writing mean things about him in her diary, which she is certain Raymond will show to him. When an elaborate box of candy arrives from Marquis, Corliss decides to make Dexter jealous, and she and Mildred fill the diary with glowing descriptions of her supposed romance with Marquis. The next day, a repentant Dexter tries to make up with Corliss, and she persuades him to take her to the Penguin Club that evening. Dexter and Corliss sneak into the club just as a police raid begins, and hide in the basement until the police are gone, only to discover that they are locked in. The Archers panic when they learn their daughter is missing, and after Dexter and Corliss finally escape through a window and return to her home, they see a police car in front of the house. Corliss swears Dexter to secrecy about their adventure and decides to fake amnesia, pretending to remember nothing that happened since she was nine years old. In the morning, Raymond delivers Corliss' diary, and her parents decide to read passages to Corliss in an attempt to stimulate her memory. Harry is beside himself when he reads the fictitious entry stating that Corliss and Marquis are engaged. Meanwhile, the entrepreneurial Raymond shows up at Marquis' office with photostats of the diary and requests that Marquis advertise in the little newspaper he is publishing. Amused, Marquis writes the boy a check, then visits the Archers and tells them that every word of Corliss' overblown prose is true. Corliss explains what happened at the Penguin Club and confesses that she faked amnesia, but Marquis, relishing the opportunity to torment Harry, persists in claiming that Corliss was with him the previous night. Neither Dexter nor Mildred will confirm Corliss' story, and when Marquis announces the "engagement" in the newspaper, Harry takes no action, fearing that his daughter's reputation will be damaged if a retraction is printed too soon. The press surrounds the Archers' home, and Raymond shares the diary excerpts with a magazine reporter, who publishes them on the front page. When her parents press her to be honest with them, Corliss feels defeated and tells them that the diary was true, and the Archers resign themselves to the marriage. They ask Corliss' uncle George, a Navy chaplain, to perform the ceremony, and when Harry gives his consent, it is Marquis's turn to be shocked. Following a glum wedding rehearsal at the Archer home, Dexter comes by and asks Harry for legal advice, explaining that he is being blackmailed by a schoolmate about the night he stayed out with Corliss. Raymond then shows up and reports that Marquis bribed Mildred to keep quiet about the diary. Harry and Dexter throw Marquis out, and Dexter and Corliss happily make up.