A relentless detective and an amateur genealogist solve a haunting cold case--and launch a crime-fighting revolution that tests the fragile line between justice and privacy. Genetic genealogy, long the province of family tree hobbyists and adoptees seeking their birth families, has made headlines as a cold case solution machine, capable of exposing the darkest secrets of seemingly upstanding citizens. But as this crime-fighting technique spreads, its sheer power has sparked a national debate: Can we use DNA to catch the murderers among us, yet still protect our last shred of privacy in the digital age--the right to the very blueprint of who we are?