A Separate Peace is John Knowles' first published novel, released in 1959. The coming-of-age novel is Knowles' most widely-known work.
Despite their polar personalities, Gene and Phineas make fast friends at Devon: Gene's quiet, introverted intellectual personality matches Finny's more extroverted, carefree, athletic demeanor.
One of Finny's ideas during Gene's "Sarcastic Summer" of 1942 is to create a "Super Suicide Society of the Summer Session," with Gene and himself as charter members. He also creates a game called "Blitz Ball" (from the German blitzkrieg, appropriate as the story is written in a World War II setting). Finny creates a rite of induction by having members jump into the Devon River from a large, high tree.
As the summer progresses, Gene becomes resentful of Finny's natural gift at athletics and of Finny's constant and distracting presence, which causes him to fail a trigonometry test. Gene convinces himself that Finny, who is the best at athletics, doesn't want Gene to be able to rival him in academics and is deliberately trying to destroy Gene's academic career. That night, Finny decides that he and Gene should jump together. While on the limb, with Finny about to jump, Gene bounces the limb. There is no elaboration; his actions are bluntly stated and regretted soon after they are committed. As a result of Gene's act of jealousy, Finny loses his balance, falls out of the tree, and breaks his leg. It is too late for Gene to realize that he "was not of the same quality" as Finny; that Gene is suspicious and tends to see ulterior motives where there are none. Gene contemplates his action while Finny slowly recovers.
The only time he shows any anger towards Gene is when Gene tries to confess to knocking Finny off the tree. Finny refuses to believe it, more wounded by that attempted confession in some ways than he was by the act itself. Upon his return, Finny begins to create a fantasy world of sorts around him to avoid facing the war, whose existence he emphatically denies: "Don't be a sap. There is no war." Finny is "the essence of this careless peace." (It is later revealed that Finny always believed that there was a war on, and that he denied its existence because he would never be able to fight in it.) Because his leg injury prevents him from engaging in sports activity, Finny encourages Gene to build up his own physical strength and athletic prowess. He even trains Gene for the possible 1944 Winter Olympics, which ended up being cancelled due to the war.
The action comes to a head when a group of students, led by Brinker Hadley, who suspects something darker in Gene, drags him and Finny into an empty classroom and puts them on a mock trial to "clear up any stray rumors." They try to force the two to confront the truth of Gene's guilt. Leper Lepellier (once soft and quiet, now mentally imbalanced from his experiences in the army) is called in, and he recalls the jump as he saw it, saying the two boys moved "like an engine," as in one went up and one went down. Finny, realizing Gene's betrayal, runs from the room and falls down a nearby flight of stairs, cleanly breaking his injured leg a second time.
After Finny is taken to the infirmary, Gene tries to go and see him, but he is furious with Gene and will not see him. Gene walks around the campus that night as if he were a ghost. The next morning, Gene sees Finny and they reconcile their differences: Gene admits that he made Finny fall, but only because it came from some impulse he could not control. Finny accepts this with relief and forgives him, but Gene is still unsure of his excuse. Gene leaves Finny so that he can go into surgery to set the bone. Afterwards, Gene meets up with Dr. Stanpole, who tells Gene that Finny has died. Dr. Stanpole thinks that, during the operation, some bone marrow from Finny's leg entered his blood stream and got into his heart, killing him. Gene takes the news as a shock, but never cries over Finny, believing that Finny's death was, in essence, his own death.
Gene reflects that Finny's death was a result of Gene's hatred and jealousy towards him. He explains that there is a point in everyone's life when they realize that there is evil in the world and that they must fight their inner demons to control themselves. It is at that time when one's innocence is lost forever. Only Finny was innocent, and although this made him unique, Gene believes it eventually led to Finny's demise.