On a cold January morning, Susan, a professor of biology, leaves her husband alone for a few minutes and returns to find him gone. Suffering from dementia, no longer able to dress or feed or wash himself without help, Christopher has wandered alone into a frigid landscape with no sense of home or direction. Lost. Over the course of one weekend, as a massive search for Christopher takes place, Susan's life intersects with those of two strangers: Jeff, her liaison with the police, a social worker and search-and-rescue expert shaken by his young wife's betrayal, and Corey, a twelve-year-old boy, rendered mute by a family tragedy, who has become one of Jeff's cases. While the temperature drops and teams scour the countryside with greater and greater urgency, Susan and Jeff venture into the fraught territory of their pasts - to impulsive choices and events that may have led to their present circumstances and to the painful question of whether they are to blame for their spouses' actions. Corey, too, is troubled by memories, and a secret that could affect them all. When the desperate search concludes, what it uncovers will transform Susan, Jeff,and Corey and irrevocably bind them together.