For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Bright Lights, Big City
Holden Caulfield gets a lecture from his old teacher, fights with his roommate, and decides he doesn't need to hang around his school anymore. It doesn't count as playing hooky if you're expelled anyway, right? Right. So, he heads into the city to kick it for a couple of days. Party time!
Act II
Such an Epic Fail
Holden tries to get lucky and fails. He tries to get company—from out-of-town girls and taxi drivers—and fails. He tries to sleep with a teenage prostitute and fails (and gets punched for his efforts). His one success is setting up a date with an ex named Sally—oh, wait, except that date basically fails, too. He tries to have a heart-to-heart with an old acquaintance and fails. Finally, he decides to visit the one reliable person in his life: his kid sister.
Act III
Tell Us How You Really Feel
Holden sneaks into his apartment to visit his little sister and hides in the closet when his parents come home. He seeks shelter with a former teacher, who is a wee bit too affectionate with Holden. After spending a depressing night in the train station, he decides the only solution is to run off to the woods, because duh.
But first he has to say goodbye to Phoebe. When she tries to join him, he bails on his plan. Apparently, it's one thing if his own innocence is ruined, but he's not about to be the cause of ruining hers. At the end of the novel, Phoebe symbolically rides the carousel a few times, and then we're back in the present with a Holden who (thankfully) is undergoing some kind of therapy.