When two lowlifes rob a gas station, murder the attendant, and then incinerate bystanders who are filling up their minivan, the Manceford County, North Carolina, police quickly arrest the killers at a nearby motel.

But a stubborn judge throws out the case because the suspects were not read their rights, leaving Sheriff Bobby Lee Baggett and Lieutenant Cam Richter to face the anger of the victims' families. Soon thereafter, a mysterious e-mail arrives in the department: a link to a video of one of the murderers being executed in a homemade electric chair, ending with a voice announcing, "That's one." The shocking video spreads throughout the Internet, drawing the attention of local, state, and federal authorities and national media, and putting intense pressure on Bobby Lee and Cam to find the vigilante before he claims his second victim.

Assigned to head the search, Cam finds himself resented by some of his fellow officers and subtly threatened by others. His job is further complicated by the fact that the offending judge is also his ex-wife and now - after years apart, and an uneasy reconciliation - his sometime lover. Cam's questions lead him to a remote mountain area in western North Carolina and a group of daredevils who call themselves "the cat dancers" - so named because they have tracked the last wild mountain lions in the region to their dens, where they have photographed the animals face-to-face, or died trying. Cam must hunt this group and the cats they seek, or become their next target.