In an interesting and informative manner Mr. Barr traces the history of police organization to the present, then switches to encyclopedia-type organization in treating the scientific procedures of police detection work. The reader learns the essentials of such techniques as fingerprinting, voice printing and some of the newer tests using neutron-activitation analysis and x-ray diffraction. In a few instances the explanations are sufficiently unclear that omission would have improved the overall presentation--but overall it will intrigue kids attracted by the opportunity to go inside a police lab.