During a winter season in Wind River Indian Reservation in Wyoming, expert tracker and U.S. Fish and Wildlife Service agent Cory Lambert discovers the frozen body of 18-year-old Natalie Hanson who was barefoot, without proper winter attire, miles from any building, and had a blood-stained groin. FBI special agent Jane Banner arrives to investigate a possible homicide. The next day, Jane learns from Natalie's father, Martin, that his daughter was dating a new boyfriend, but he does not know the man's name or whereabouts. The autopsy shows blunt trauma and sexual violence and confirms Cory's deduction that the girl died from exposure, specifically pulmonary hemorrhage caused by rapid inhalation of sub-zero air. However, the medical examiner is unable to confirm the death as a homicide, therefore preventing Jane from calling in an additional FBI investigative unit.