By every conventional measure, Jessica Knoll’s thriller, “Luckiest Girl Alive,” was a wildly successful literary debut. It sold more than 450,000 copies and spent four months on the best-seller lists. Foreign rights sold in more than 30 countries. The actress Reese Witherspoon optioned the film rights, and Ms. Knoll wrote the screenplay.

Still, Ms. Knoll couldn’t escape the nagging feeling that she had let her readers down. Even though her book was fiction, she felt she hadn’t fully told the truth.

The white lie she told over and over, at readings and book signings and in interviews, was complicated and hard to untangle. She assured fans that some of the darker elements of her novel, which centers on a successful young woman who struggles with the lingering trauma of a sexual assault, were purely fiction. She deflected questions from readers who wanted to know how she had managed to portray a rape and its aftermath so vividly and realistically, saying she had heard stories from friends and classmates.

She is no longer dodging those questions. On Tuesday, Ms. Knoll published a raw and chilling essay describing how the gang rape depicted in her novel was drawn from her own experience in high school, when she was sexually assaulted by three boys at a party, and then tormented by classmates who labeled her a slut.