Smallpox has been extinct -- the only species ever deliberately exterminated by humankind -- since 1977. So why has it suddenly turned up in Sheridan, Wyo.? Bullheaded county coroner Dr. Samantha Turner (A Clinic for Murder, 1993, etc.) is hot on the trail of the infection that killed David Crider, just returned from a student leadership conference in Washington, D.C., when she's felled herself, apparently by a treacherous hantavirus that's running rampant among everybody who treated David. Sam spends ten days in the hospital, emerging weak, shaken, and frustratingly amnesiac. Why would anybody deliberately let loose smallpox among a bunch of high-school kids? What does the real threat of a new smallpox epidemic have to do with the bogus epidemic of hantavirus? How are Sam's husband, Derek, and his CIA bosses involved? What's happened to David's best friend, Jess Gorzalka, who's practically certain to be infected with smallpox, and to Sam's father, an Alzheimer's patient vanished from his nursing home? And how can Sam keep the outbreak secret when new cases are threatened every day that brings Sheridan's college rodeo closer? Landreth has no serious rivals in the niche of intense, low-calorie (cf. Robin Cook's double-scoop, high-cholesterol thrillers) medical-ethics whodunits. Here it's hard to tell who's more diabolical, the killers or the feds.