Driven by moral outrage and deep personal demons, Arizona private inspector Lena Jones enters the brutal world of polygamy when she is hired by a frantic mother desperate to rescue her thirteen-year-old daughter from a polygamist sect on the Utah border. The girl is about to be married to the compound's sixty-eight-year-old leader, Solomon Royal, in a trade brokered by her father in exchange for two sixteen-year-olds.
The snatch goes off without a hitch, until Lena stumbles over the dead body of Brother Royal, and the girl's mother is charged with his murder. To find the real killer, Lena goes undercover as the new "wife" of an inside sympathizer and infiltrates the dark reality of Purity-where misogynistic men and frightened women share a deadly code of silence. As Lena gets closer to the monstrous secret at the compound's heart, the nightmare of her own childhood takes a strange turn as the disparate natures of good and evil converge in shocking new ways.