In the spring of 2005, the gruesome murder of two teenagers in Great Falls Park -a majestic, heavily forested national park near Washington, D.C.-begins an investigation by U.S. Park Police Detective M.J. Powers that will lead her into the darkest corners of the human mind and test her both professionally and personally. A lifelong distance runner, M.J. begins doing her daily runs in the park believing that the murderer may frequent its trails. When she learns of a strange figure seen moving through the park at night during a thunderstorm, the otherwise scenic landscape becomes an ominous backdrop as she seeks to solve the mystery. Driven to find the killer before he strikes again, she enlists the help of a homeless Vietnam veteran, a dedicated park ranger and her partner-who is also her lover-in uncovering the dark secret behind the murders.