Black Klansman: Race, Hate, and the Undercover Investigation of a Lifetime written by Ron Stallworth. Paperback.

"Black Klansman is an amazing true story that reads like a crime thriller, and a searing portrait of a divided America and the extraordinary heroes who dare to fight back. When detective Ron Stallworth, the first black detective in the history of the Colorado Springs Police Department, comes across a classified ad in the local paper asking for all those interested in joining the Ku Klux Klan to contact a P.O. box, Detective Stallworth does his job and responds with interest, using his real name while posing as a white man. He figures he’ll receive a few brochures in the mail, maybe even a magazine, and learn more about a growing terrorist threat in his community..."