Kathy Bardy and Julia Redmond have been best friends since first grade in spite of vast differences in their backgrounds and talents. Julia is wealthy, beautiful, and an only child who does well in school without trying hard. Kathy's middle-class parents both work in the family business; she has a younger brother and sister, and she struggles through school. When the book opens they are ending their freshman year in a public high school.

Kathy had never played tennis until her talent was discovered at a tennis clinic. An eccentric tennis coach encourages her, takes her on for private lessons, and arranges for her to work at the club to pay for her membership. Kathy trains for at least twenty hours a week and works long hours at the club. With the exception of outbursts of temper that come quickly and uncontrollably when angered, Kathy finds it difficult to talk about her emotions. Kathy finds school difficult, especially algebra (a course the author failed three years in a row). Although she would never cheat in tennis, Kathy cheats in order to pass the algebra exam. She is caught and must spend the summer being tutored by the algebra teacher and must retake the exam. At the retake of the exam, Kathy struggles with the temptation to cheat again. She receives conflicting messages from adults in her life about the relative importance of school and tennis. Kathy's serious self-examination of the role of competition in her life permeates the book.

Julia's life has been easy. She does not know what it is like to work for something; even good grades come effortlessly. She is not jealous of Kathy's success and she is the only person with whom Kathy can let her guard down and talk about the pressures and frustrations of competition. Julia senses what Kathy needs, and Kathy runs to her whenever things go wrong.

Marty, the tennis coach, describes herself as mean, as someone no one likes. Tennis appears to be her entire life. At only one place in the book does she appear in anything other than tennis whites. She is a critical taskmaster who demands more and more of Kathy. She is never satisfied and never offers praise. Winning is very important to her, but so is good sportsmanship. She says, "Cheating is stupid."

Jody, Kathy's younger sister, resents the family sacrifices necessary for Kathy to pursue tennis. She accuses her sister of being "lethally competitive." Nevertheless, she does her part and is loyal to Kathy when it really matters. Another important figure is Oliver English, a skinny seventeen-year-old student at Yale, who becomes an instant friend of Kathy's. He speaks to Kathy honestly and causes her to think about the role of tennis in her life. A key figures is Ruth Gumm, a tall, awkward girl whose main talent in tennis is her strength. She surprises Kathy by defeating her and becomes Kathy's nemesis. Her drowning fills Kathy with guilt over her treatment of Ruth, then fear that others will think she was responsible for Ruth's death.

Competitiveness is the central theme of the book. A realistic view is provided of the time commitment necessary to compete successfully in tennis and of the financial burden. The emotional effects of competing are described throughout the book. The cost of winning is examined from Kathy's perspective and also from the perspectives of her sister and her friends.

Although this novel is technically a mystery, solving the puzzle of Ruth's drowning is secondary to the theme of competitiveness. Kathy wants to clear her name even after officials have ruled the death accidental. She is more concerned with establishing an alibi than in discovering who, if anyone, is responsible for the death.