John Knowles’s novel A Separate Peace is the tragic coming-of-age story of Gene Forrester, whose first-person narrative recounts his prep school memories from fifteen years ago. As Gene narrates events through the vehicle of flashback, he also inserts his own retrospective philosophical musings, and this shifting perspective, as well as Gene’s reticence, suggests that he may be an unreliable narrator. 
The novel explores the difficult transition from childhood to adulthood, with the conflicts and horrors of World War II lurking symbolically in the background. Knowledge of the war’s unsettling events infects many images and scenes in the novel, encroaching on the illusory “separate peace” of life at the Devon School in New Hampshire. By exploiting this disturbing setting, Knowles suggests that human maturation involves the wisdom gained from recognizing one’s internal conflicts and then battling them, seeking resolution, sometimes unsuccessfully. In A Separate Peace, Gene grows to recognize his own resentments and jealousy toward Finny, yet he is unable to overcome them. In an era filled with hostility and fear, Finny’s innocence and heroic character emphasize the tragedy of his eventual death, while Gene survives to reflect on, suffer with, and learn from his own confused and unresolved feelings toward his friend.
The novel begins in the summer session of 1942, when all rules seem to be suspended, a metaphorical backdrop of liberty and psychological innocence, and Gene becomes close friends with Finny, his mischievous and handsome roommate, who has an innate charisma and exceptional athleticism. Gene’s internal conflict manifests as a division between his admiration and his resentment for Finny, which grows as the story progresses. Gene is jealous of Finny and his athletic abilities, and the novel’s central conflict develops through his struggles with both love and hate for Finny.
The rising action reveals that Gene’s jealousy is growing, although Finny lacks resentment and is incapable of envy. Though uncompetitive, Finny’s fatal flaw is that he is self-involved, and Gene does not resist his influence; he is not brave enough to say “no.” Thus Gene’s sense of self is subsumed by Finny’s stronger one, and Gene does things he does not want to do; the power dynamics are in Finny’s favor. Most notably, Finny convinces Gene to make a dangerous jump out of a tree into a river, which becomes their ritual. Plagued by resentment and paranoia, Gene begins to suspect that Finny is trying to sabotage his studies.
In the climactic event of the novel, the two go to the tree for their jumping ritual, and when Finny reaches the edge of the branch, Gene’s knees bend causing the branch to shake. Finny, the athlete, falls and shatters his leg. Though the jostling of the branch remains mysterious, the fall answers a deep wish within Gene. By crippling Finny, he has brought him down to his own level. Edenic life is shattered as the darkness of the human heart is revealed; the two fall prey to the goods and evils of adulthood. 
While the tragedy is considered an accident, the falling action of the novel suggests otherwise. The doctor tells Gene that Finny’s athletic days are over, and Gene feels guilty, insisting that he is culpable for what has happened. Finny refuses to accept Gene’s confession, since he ultimately cannot sever himself from his friend, a marked indication of their codependency. Gene attempts to transform himself into the athlete that Finny was—to turn himself into a mirror of him—by training for the Olympics in his place and trying on his clothes. As these events unfold, Finny’s injury becomes his “separate peace.” He will not have to go off to war, and he becomes hostile with anyone who challenges his self-preserving denials; he does not understand the concept of an enemy. 
Meanwhile, a friend named Leper Lepellier has gone to war, deserted, and begins going mad—his experience makes the war all too real. When he calls upon Gene to visit him in Vermont, he claims that he was present at Finny’s accident and knows what Gene did. Back at Devon, at a tribunal regarding the accident overseen by their classmate Brinker, Leper implicates Gene. When Finny rushes out of the room, he falls again on the marble stairs and once again breaks his leg.
Gene sneaks in to visit Finny in the hospital and the two are reconciled. As a doctor operates on his leg, some marrow detaches from the bone and enters Finny’s bloodstream, traveling to his heart and killing him. Arguably, the marrow symbolizes Gene’s underlying resentment that plugs Finny’s heart. Gene receives this news tranquilly; at the funeral, he thinks about how he is a part of Finny and will always be with him since their personalities have become so wed to each other. 
In the novel’s resolution, soldiers set up camp on campus, and World War II ceases to be an abstraction. The war comes to represent an individual’s personal war both to defend and end all childhood illusions of a friendly world, replacing them with discovery of the “enemy.” As the work concludes, Gene reflects on the effects of constant enmity upon the human heart, believing that only Finny had been immune to such painful awareness.