A thirteen-year-old boy named Brian Robeson is flying in a small plane over the Canadian wilderness, with only a quiet middle-aged pilot for company. Brian is consumed with thoughts of his parents’ divorce and the way it has torn his life apart, and he is unable to stop thinking about it even when flying over the beautiful landscape. Brian also hints at knowing what he calls “The Secret” about his mother, which his father does not know. Brian is briefly distracted when the pilot gives him a turn at the plane’s controls, but he soon falls into miserable contemplation of the divorce again. The reader learns that Brian lives in the New York City area but is on his way to visit his father in Northern Canada, since his father now has summer visitation rights. Brian feels angry at his mother, but somewhat guilty for refusing to talk to her in the car on the way to the airport. He remembers that she gave him a new hatchet as a gift for the journey, which he is wearing on a loop attached to his belt.
The pilot starts complaining of aches in his shoulder and stomach, which distracts Brian from his thoughts. The pilot suddenly spasms violently, and Brian realizes that he is having a heart attack. The pilot falls unconscious, leaving Brian alone in the airborne plane. Terrified, Brian realizes that the pilot’s spasms knocked the plane off course, and he tries to steer it back in the right direction. He desperately calls for help on the radio but cannot get a clear connection. An hour passes, during which Brian realizes that the pilot is definitely dead, and he will have to land the plane himself. The plane abruptly runs out of fuel and starts to drop. Brian manages to steer the plane toward a lake at the last minute, landing in the water although the wings are torn off in the trees on the way.
In a panic, Brian escapes from the sinking plane and manages to swim to the shore of the lake, where he falls asleep. When he wakes up, the first thing he remembers is discovering his mother in the car with a strange man while out biking with his friend Terry. This is The Secret that haunts him. Remembering the crash, Brian starts screaming and crying. He does not know where he is and is in terrible pain. Brian loses consciousness again and wakes up in the early morning, still in pain and confused. Brian cannot stop thinking about the pilot’s death and is unable to move, especially after he is attacked by mosquitos that appear as the sun rises. Before falling asleep again, Brian struggles to take in his surroundings and sees a blur of lake and trees, as well as a tall rocky ridge.
When he wakes up, Brian is horribly thirsty and sunburned, and he decides to drink the lake water even though it might not be safe. He tries to calm himself down, but keeps thinking that he is nowhere and has nothing. He focuses on repeating his own name and telling himself that rescuers are likely to come for him soon. He remembers an English teacher named Perpich who always used to tell students to get motivated and stay positive. The memory inspires Brian to carefully look through everything he has, which makes him remember the hatchet. He also remembers that he himself might be his most important asset. As Brian considers his situation, he realizes that because the plane was off-course, rescuers might not come right away. However, he decides to build a shelter and find food, determined to survive until they find him.
Brian discovers that the stone ridge hides an overhang by the lake, which he decides to turn into a shelter, happy at his good luck. Extremely hungry, Brian sets off around the lake to look for berries to eat, which he finds by following a flock of birds. Although the berries are tart, he eats many of them and harvests more to bring back to his new shelter. In the night, Brian wakes up horribly ill from eating the berries and is again lost in thoughts of his mother’s affair. The next morning, he is overcome with self-pity for how lost, alone, and ugly he is, feeling unable to escape his misery. Eventually, his hunger distracts him, and he eats a few of the riper berries before going to search for better food. As he leaves, he catches himself thinking of his shelter as home.
Along the shore of the lake, Brian finds a clearing full of raspberry bushes but is startled when a black bear appears. However, the bear leaves him alone, interested only in the berries. Brian realizes that it does not pose a threat to him and continues gathering berries. Later, he wonders how the bear felt seeing him and realizes that he has stopped thinking about his own pain for the first time since the crash.
While Brian is sleeping that night, he hears an animal enter his shelter and throws the hatchet at it. He misses, and the animal, which turns out to be a porcupine, attacks his leg. Brian begins to cry and feel sorry for himself again, a point that he later recalls as the moment in which he realized that self-pity doesn’t work. Brian has odd dreams of his father and his friend Terry, and when he wakes up the next morning, he suddenly remembers seeing the hatchet make sparks when he threw it against the rock wall in the night.
Brian succeeds in recreating the sparks, becoming totally absorbed in the task of making fire. After some trial and error, he succeeds in getting the sparks to catch in a nest of birch bark, creating fire at last. Brian is overjoyed and gathers wood for the fire, swearing to himself that he will never let it go out. Soon thereafter, he discovers that a turtle has laid eggs in the sand near his shelter, giving him a new source of food. Encouraged by the fire and food, Brian begins to feel more confident about his ability to survive, but reminds himself that he must keep hoping to be rescued as well.
In order to keep from getting depressed, Brian resolves to stay busy around his camp by cleaning, gathering wood, and collecting food. He also makes an unlit signal fire on top of the ridge, in the hope that he can send a smoke signal if he hears a passing plane. Brian feels himself changing mentally, becoming more attuned to his surroundings and noticing everything more than he did living in the city. He also realizes that lots of fish live in the lake and plans to make a spear in order to catch them.
When his fish spear doesn’t work, Brian decides to build a bow using springy wood and one of his shoelaces. While cutting wood for the bow far from his shelter, he suddenly hears the engine of a plane. Ecstatic, he sprints back to light the signal fire, but the plane turns back just as he gets the smoke going. Realizing the plane has disappeared, Brian falls into total despair, feeling certain that he cannot survive on his own any longer.
Many days later, Brian stands in the shallows of the lake, fishing even though he is sick of eating fish. Moved by instinct, he turns to see a wolf behind him on the hill. Though he is initially frightened, Brian quickly realizes that the wolf is only a part of nature and does not want to harm him. The reader learns that 42 days have passed since Brian’s despair at the plane’s passing. The narrative flashes back to that experience, during which Brian attempts to commit suicide with the hatchet before deciding that he has to continue living. Afterward, Brian realizes that he is not the person he was before the crash and must now rely on himself to survive.
Brian experiences many setbacks and mistakes as he learns to live in the wilderness, and he views his mistakes as learning experiences. He successfully builds a bow and learns to shoot and cook fish, which gives him the strength to believe he can keep surviving on the “tough hope” of self-reliance. Several times, Brian’s mistakes seriously threaten his survival, as when an encounter with a seemingly harmless skunk almost blinds him. Still, each mistake helps Brian improve his survival skills, and over time he even learns how to hunt and kill some of the birds that live in the woods. He comes to realize that his survival depends on his ability to be patient and attuned to his surroundings.
Back in the present, Brian has succeeded in building a sustainable life in the wilderness, even though he remains hungry and vulnerable. As he is hunting that morning, a moose attacks him for no reason, severely injuring his ribs and leaving him terrified. He returns to his shelter to recover, but that very same night, a tornado strikes, destroying his camp and scattering his possessions. Brian marvels at how quickly his luck can change, but he also finds himself feeling more resilient than he once was, vowing to rebuild the camp even as the tornado tears it apart. When he wakes up in the morning, he sees that the tail of the sunken plane is now visible above the water and prays for the pilot to have rest.
Brian begins rebuilding his shelter and camp. As he does so, he suddenly remembers that survival pack in the plane and wonders if he can get to it now that part of the plane is above the water. He decides to explore the plane, making a crude raft to stand on in the water. He uses his hatchet to open a hole in the plane, at one point dropping his hatchet into the lake. Although he fears that it is lost forever, Brian successfully retrieves the hatchet from the bottom of the lake, and soon opens a hole in the plane wide enough to crawl inside.
Floating amid the supports of the body of the plane, Brian dives down and quickly finds the survival pack. In the process, he sees the decaying head of the pilot, mostly eaten by fish. Brian is horrified, but he manages to get himself and the survival pack out of the plane and, eventually, back to camp. Exhausted, Brian falls asleep immediately.
The next morning, Brian opens the survival pack and can barely comprehend the incredible riches it holds, such as sleeping bags and packets of food. There is even a rifle, which makes him feels strangely separated from the natural world around him. He sets the rifle aside and finds an emergency transmitter as well. He flicks it on, but it appears to be broken. Overwhelmed by the excitement of the food, Brian decides to have a feast before rationing the rest, and begins to cook several packets over his fire. Suddenly, a rescue plane lands on the lake. The pilot of the plane asks if he is the missing kid and Brian, astonished, invites the man to eat with him.
In the epilogue, the reader learns that the pilot heard the signal from the transmitter that Brian unknowingly left on. Brian returns home to find that he is profoundly changed and experiences life in a much calmer, more observant way than he did before. He often dreams of the lake and its beauty. Although his parents are happy to have him home, they do not get back together, and Brian’s life soon returns to normal. Although he considers it, he does not tell his father about The Secret.