In 1987, respected cartographer Helen Voss vanished from her locked office at the National Geographic Society, leaving behind only a hand-drawn map of a place that didn't exist. Thirty-five years later, a retired park ranger's deathbed confession would reveal how one woman's expertise became the key to her own disappearance—and how the very skills she used to chart the world were turned against her by someone who knew exactly where to hide a body.