The story starts out with 9-year-old Trisha McFarland going on a hike with her brother and her recently divorced mom. Her mom, who is determined to give the kids a good time on the weekends together, dragged them to go on a six-mile hike on the Maine-New Hampshire branch of the Appalachian Trail. Her brother, Pete constantly fights with their mom since he’s unhappy that they moved from Boston to small-town Maine. While hiking on the trail, Pete and their mom started bickering like usual, Trisha who had to go to the bathroom and was sick of hearing them argue, stepped off the trail for a little bit. She wanders a little too far off by herself, and tried to take a short cut back to the trail but soon realized that she was lost in the wilderness.
While in the wilderness, she thinks about her loved ones: her Dad, who was the perfect father until his beer habit ruined him, her loving but stubborn Mom, and Trisha’s best friend, Pepsi Robichaud and her saying “Don’t go all GIRLY on me, McFarland!” It was tough for her since she had to improvise, and try to remember hiking and camping tips her mother used to give her to survive.
After the first night in the wilderness, she started having hallucinations, both good and bad, and drifting in and out of the real world. The bad one was the monster that she imagined that watched her every day while she slept, and sometimes followed her, whom she named the God of the Lost. After walking a few days, she started to find cruelly slaughtered animals and claw marks on the trees. The good hallucination was Tom Gordon, the baseball player who she loved and adored. He always popped up when she needed help, or when she was afraid. Her Walkman was the one thing that kept her sane, voices in the wilderness calmed her. It made things seem normal. Her favorite thing to do was to listen to the baseball games and cheer for Tom Gordon, pretending she was there at the ballpark, actually watching him play.
Nine days later, she somehow ended up walking until she was just about 4 miles from New Hampshire Route 96. There, she knew she had to face the God of the Lost who finally came out, and let her see it. The last thing she did, before a hunter came and found her, was through her Walkman at the God of the Lost baseball-style. The man then shot his rifle at the thing that he later questioned if it was a bear or something else. Turned out that Trisha’s disappearance was all over the news. She was then brought to a hospital, where her worried parents and brother came to see her, each of whom blamed themselves for her disappearance.