Dog behaviorist Mara Ellison is hired by the wealthy Ashford family to deal with Bishop, their rescue pit mix: every night at 3 a.m., the dog stands in the children's hallway, hackles up, blocking the doors. The family calls it aggression. But Bishop was a yard dog at a fighting operation - he doesn't fight, he watches - and Mara begins to understand he isn't guarding against the children. He's guarding them.