The novel begins with our narrator returning to the Devon school, a prep school where he boarded as a high school boy.
He's disappointed to find that the school appears preserved, unchanged, even newer-looking; he thought it would be aged these fifteen years later.
Along with the unchanged buildings the narrator finds an unchanged emotion: fear. He never recognized it then, so the fact that he does now must mean he has escaped from it, he concludes.
The month is November. Accordingly, since this is in New Hampshire, it's grey and wet. The narrator walks through said grey wetness to the First Academy Building, describing the school grounds in lovely literary detail, which you should check out.
Once in the Academy Building the narrator draws our attention to the famous marble stairs inside, which are so hard that, despite their age, they are barely worn down in the centers.
He realizes that he's grown over these past fifteen years, and as such everything around him looks smaller. (Funny how that works.)
Walking around the grounds some more, the narrator notes that Devon has "changed and harmonized" with everything around it; he hopes he can achieve the same transformation himself, or perhaps that he already has.
But now it's time for the narrator to visit the place that he came back to Devon to see. He makes his way past the school's playing fields to the river and trees at its banks.
He finds "the tree" – the one he has been looking for – and notes that, just like the school grounds, this too looks smaller now that he himself has gotten bigger. It looks aged and weary, and the narrator quotes a French adage, "The more things stay the same, the more they change after all." (Actually, the normal adage is the other way around, but the narrator reverses it here.)
Now there's a nifty little hint about a "death by violence," just in case you fell asleep somewhere between the marble staircase and the tree. The narrator heads back in out of the rain, and we head back in his memory to his days as a schoolboy at Devon.
We cut to the narrator as a boy standing in front of the tree with his crazy buddy Phineas. He doesn't want to climb it; Phineas thinks they should. (Get used to this dynamic.)
Phineas thinks the tree is "such a cinch" (meaning it's easy, in case you're not as up-to-date on your 1940s slang as we are. Did we mention this is the 1940s? Because it is. 1942 to be exact.)
The narrator (as a boy that is), meanwhile, is being sarcastic. It's his sarcastic summer.
There are three other boys there with them, all contemplating the tree jump. The boys are in the Summer Session at school before their junior year (when they will be referred to as "Upper Middlers").
Phineas starts to undress for the jump (which, if you hadn't gathered by now, ends in the river). The narrator comments on his physique: though he's the best athlete in the school, Phineas (or "Finny") isn't marvelously built. He's about 5'8 and 150 – ten pounds more than our observant narrator here is at the time.
Finny climbs to the top of the tree and leaps off into the river. Not to be outdone, the narrator follows, pausing at the top for purposes of drawn-out suspense and adolescent panic. He notes that the ground is directly below him; in order to hit the water and not scatter his brains on the dirt, he has to jump out a fair way.
He does jump, but not before some internal resentment boils up, directed at Finny for getting him into this mess in the first place.
Once out of the water, the narrator is greeted by Elwin Lepellier (one of the three other boys) who is commonly known as "Leper." (Oh, high school nicknames.)
The other three boys – Leper, Chet Douglass, and Bobby Zane – are too scared to jump. So it's just the narrator and Finny who have accomplished the feat. "At that moment," says the narrator of himself and Finny, "we were the best of friends."
As they all head away from the river, he describes Finny's walk as a fluid, rolling movement. Finny, we are told, resents rigidity and authority.
The boys hear the dinner bell and hurry back, but Finny and the narrator stay behind to wrestle and generally mess around, à la all adolescent boys that have ever lived.
The narrator describes more of the school as he and Phineas finally return to their dormitory. Because it's the summer session, there are only about two hundred students around – most of the campus is empty. Even the headmaster is away.
Back in the room, the pair (who are roommates, by the way) get to their Thomas Hardy-related homework while listening to their illegal radio.