This comprehensive, sometimes critical and often dry history explains how the Secret Service grew out of the Treasury Department in 1865, with the original mission of protecting American currency against counterfeiters. Melanson, an expert on political violence and government secrecy, and Stevens (The Voyage of the Catalpa) show how, late in the century, the Service gradually (and initially without congressional authorization) expanded its mission into presidential protection. Opponents of the expansion thought assigning a guard to the president would give him the trappings of monarchy, making him less accessible to the people. The most compelling chapter examines the failure that continues to haunt the agency: the 1963 assassination of President Kennedy. The authors analyze what went wrong in Dallas: Kennedy's limo driver reacted too slowly to the first bullet, failing to take evasive driving action so as to avoid the second, fatal shot. Moreover, according to the authors, Kennedy's death was a failure of intelligence-sharing between the Secret Service and the FBI. Following the assassination, the authors argue, the agency "began a pattern of lies about its fatal missteps in Dallas." All aspects of the agency's work are covered extensively: recruiting, training, intelligence gathering, the often-tense relationship between the agency and the people it tries to protect. President Johnson, in particular, rebelled against Secret Service restrictions, once literally pissing on an agent. This is a worthwhile book for assassination buffs and those with an interest in the inner workings of government. (Nov.)