Dated. Written in 1966 for a YA audience. A collection of short biographies of historic detectives from the 1820s through J Edgar Hoover in the 1950s. Pre DNA, pre cell phone, pre computers. Naive presentation of police techniques impinging on human rights. No discussion of the death penalty, racial disparities, or white collar crime. One postitive was the increased emphasis on teamwork, as the profession evolved. This book is only important as a reflection on attittudes toward law enforcement in the 1950s.