Brian Robeson, a thirteen-year-old from New York City, boards a plan headed from Hampton, New York to the Canadian north woods to visit his father. His parents' recent divorce weighs heavily on him, as does "The Secret" that his mother is having an affair. The pilot gives him a very brief flying lesson in which Brian has control of the plane for a few minutes. The pilot seems to be experiencing increasing pain in his shoulder, arm, and stomach. At first Brian does not think it is very serious, but as the pilot begins jerking in his seat it becomes clear that he is having a heart attack. The attack stops and the pilot is dead; Brian is forced to take over the controls. After a harrowing descent, the plane crashes into a lake in the Canadian woods, where Brian is stranded.
Brian has little to eat and is injured from the crash, but believes he will soon be rescued. He finds some strange berries to eat, which make him extremely sick. He then finds a raspberry patch, where he spots a bear. Brian constructs a shelter and in the middle of the night he hears a noise. A porcupine has entered his shelter and Brian throws the hatchet in its direction. It shoots its quills into Brian's leg, causing him severe pain. Brian attempts to build a fire with no matches and eventually succeeds when he learns how to strike his hatchet against a stone to ignite sparks. He finds turtle eggs and eagerly eats them. One day a plane flies overhead but does not see him and continues on its way, leaving Brian devastated and hopeless. He attempts to commit suicide by cutting himself with his hatchet, but survives the attempt and emerges from the experience determined to embrace life and to take an active role in his own fate.
Brian soon catches his first fish and enjoys a big feast. That night, however, a skunk enters the shelter and when Brian yells at the skunk, it sprays him, temporarily blinding him and covering him with a horrible stench. Brian perfects his tools and catches a foolbird, his first meat. While he is cleaning the bird in the water, a moose attacks Brian, injuring his ribs and his shoulder. Another unfortunate incident soon follows when a tornado sweeps over the woods and destroys Brian's shelter.
The day after the tornado, Brian discovers that the chaotic storm has riled up the water in the lake, and the tail of the plane had emerged from the lake, reminding Brian of the dead pilot and compelling him to say a few words for him. Lying in bed one night, it occurs to Brian that he could seek out the survival pack in the body of the plane, and he determines to build a raft to do so. After many incidents of trial-and-error, Brian retrieves the survival pack from the plane. At one point he drops the hatchet to the lake's bottom, but retrieves it with a long dive. On his way back up to the surface, Brian sees the dead pilot's head underwater, partially eaten by fish. Brian gets sick in the water but manages to make it back to his shelter to get some sleep.
The next morning Brian opens the survival pack, which contains countless useful items, some of which Brian rejects in favor of the self-sufficient methods he has developed during his time in the woods. However, there is freeze-dried food that he decides to cook immediately. He also finds something labeled "Emergency Transmitter." He fiddles with it but it appears not to function. As Brian is preparing his much-anticipated meal, a plane lands on the lake to rescue a dumbfounded Brian sitting down to eat his freeze-dried meal.