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.