After assassination took three American presidents in thirty six years, Americans overcame their distaste for body-guards about their leaders and the Secret Service came into being. This history of the Secret Service, and the investigations it conducts to fulfill its primary function,- protection of the President, has the same gripping behind-the- scenes flavor that distinguished Quentin Reynolds' account of the FBI. Significant details here do the trick. The author introduces us to Room 98 in the White House, where for seventeen years each crank or threatening letter addressed to the President has been cross-indexed, filed and photographed. He recounts an attempt made on Roosevelt's life and the recent close call Truman had at Blair House. The exhaustive precautions taken to guard the Presidents -- sometimes against their will -- make exciting reading. There is the truck labeled Explosive in which suspicious packages are placed for detonation. And there was the deadly letter sent by King Harry I of Harrisonia demanding annexation by the United States. (He turned out to be a small boy who had been sold one inch of Alaska in exchange for boxtops.) The author devotes substantial space to the work of the Secret Service in prosecuting counter-feiters and forgers but the best reading is in the comprehensive accounts of the detective work done in tracking down threats, both innocuous and portentous.