“The Bitter Past,” by Bruce Borgos (Minotaur Books) “The Bitter Past,” by Bruce Borgos (Minotaur Books) As sheriff of a small Nevada town near Las Vegas, Porter Beck spends most of his time on trivial crimes — until a retired FBI agent is found tortured and murdered. Within hours, a gorgeous (of course) female FBI agent shows up and confides that the dead man had been gathering information on a KGB spy who stole secrets from a Nevada test site 60 years earlier. It seems the Russian, who was supposedly killed in a nuclear accident, may not be dead after all, and he’s living in Beck’s jurisdiction. So Beck has to find the aging Russian before the assassin does.