With her own department working against her, Homicide Detective Alexandra Danvers is determined to bring child killer, Arthur Book, to justice, no matter the cost.

Police corruption specialist, Detective Xavier Knight, a man without a home, friends, or family, is asked to evaluate Lexi's fitness for duty while undercover as her new partner. He fears his actual mission–investigate Lexi–could allow a monster to walk free.

Though holding tight to their own secrets, they launch a covert investigation into Arthur Book who could cost Lexi and Xavier their careers, and possibly their lives.