The strange thing about re-reading books you read in high school is how your age and (I assume) wisdom, changes how you view the book. I remember reading this and despising Phineas and Gene. I didn't know why I didn't like them, I was a dumb teenager, but I didn't like either of them.
After a re-read, I still do not like Gene but Finny has a pass. I realize, now, that the codependency of the two is what led me to not like either of them. I've never been a codependent person, never needed someone around all the time. I don't need to be a leader, I don't want to be a follower. Relationships like this have always irked me. But now I see that Finny became codependent out of necessity. Gene still sucked.
Set in a boy's school in New England, Gene and Finny are roommates and best friends. Finny's personality is outgoing, confident and incorrigible. Gene is meek, quiet and self-loathing. The leader-follower relationship is set. As Gene becomes more envious of Finny, he causes a deliberate accident that causes Finny to shatter his leg, thus ending his athletic dreams. Shitty move, Gene.
Finny eventually comes back to Devon, the same but crippled, and is forced to rely on Gene. Gene is still hating himself for what happened (which he should) and actively delves into daydreams and trying to become "Phineas" for Finny. Keep in mind that while this is all happening World War II is going on and each student at Devon is in danger of being drafted. The book never goes near the war, it just keeps it as a dark cloud over everyone and influence their decisions.
Just to keep the spoilers at bay, know that Finny and Gene's story gets more complicated with help from Brinker, another self-important student at Devon. Things do end badly and lessons don't entirely seem to get absorbed.
I couldn't remember anything about this book when I picked it up, except that I read it and it was set at a boy's school. Each page gave me deja vu and I realized it was there all along. I just didn't realize the plot I had in my mind was to A Separate Peace.