It Happened to Nancy was written for young adults by Beatrice Sparks from the notes of an anonymous young girl whom Sparks names 'Nancy.' The book opens when Nancy is fourteen years old and regularly sick with asthma. At a Garth Brooks concert, Nancy meets an eighteen-year-old boy named Collin who is kind and loving to her. Nancy is overwhelmed with love for him and thinks that he has changed his life forever and for the better. Collin eventually seduces Nancy, gets her drunk, and rapes her in her own house. After trying to recover psychologically, Nancy finds herself getting sicker and eventually finds out that Nancy had HIV.

Nancy faces a horrible tragedy but she is fortunate enough to have a loving mother and several very close friends called "the gaggle," that consists of Nancy, Dorie, Red and El. They also spend time with a popular, handsome, and honorable boy named Lew who Nancy eventually starts to date and falls in love with. In contrast to Collin, Lew is not out to seduce Nancy and would never hurt her. In fact, he makes them both promise to not have sex until they are married. Nancy's father, who lives in Phoenix while she and her mother live in South Carolina, also cares for Nancy deeply and does what he can for her when she stays with him. Nancy also has several supportive doctors throughout her illness and many hospitalizations. Even when Nancy withdraws due to depression, her friends and family are there for her, as are the comforts of her faith.

Nancy quickly declines from HIV to AIDS due to an already weak immune system. The book is set in the early 1990s before the discovery of drugs that block the HIV virus from becoming AIDS. At that time there is no effective AIDS treatment. Nancy is going to die and it is only a matter of when. Nancy is naturally a happy and bright teenager and handles her decline surprisingly well. She remains upbeat when she can, although she is of course frightened and in pain throughout much of her illness. Near the end of her life, Nancy spends a final few weeks living with her aunt and uncle in Idaho on a ranch, which practically functions as hospice care.

It Happened to Nancy is composed of Nancy's diary entries throughout the years of 1992, 1993, and 1994. The author, Beatrice Sparks, includes an appendix full of information about HIV and AIDS for young adult readers.

Controversy surrounds It Happened to Nancy due to accusations that it is not a genuine non-fiction work. Some have questioned whether Sparks wrote the book simply in order to raise AIDS and date-rape awareness. A number of important errors fill the book that indicates either the author's sloppiness or its falsification. Nonetheless, It Happened to Nancy is a powerful work that promises comfort to teenagers with HIV and AIDS and information for other teens to prevent them from being infected.