Gidget Lawrence, fifteen and a half years old, falls in love with Jeff, a college student, and takes up surfing to be with him. Gidget has a healthy, trusting relationship with her widowed father, Russell Lawrence, an English professor. However, Gidget's married sister, Anne, constantly checks on Gidget. In this, Anne is abetted by her husband, John Cooper, a student psychiatrist. Anne comes upon Gidget's diary and reads of a romantic episode, described with lurid overtones. Anne and John immediately relay their find to Russell. Slightly worried, Russell discusses possible problems that may have arisen for Gidget. When Gidget finally learns what he is referring to, she points out that the incident is entirely imaginary, being dated for the following day. Russell agrees to go along when Gidget writes another postdated entry, stating she is about to end it all. On reading it, Anne and John rush to the beach with Russell in tow. There, Jeff has been playing up to another girl to annoy Gidget. With the help of her friend, Larue, Gidget reaches an understanding with Jeff. Anne and John are embarrassed by the way they have been misled, but it is apparent that despite Russell's warning, they will not stop trying to run Gidget's life.