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
Welcome to Pnin land
We meet Pnin, our belovedly strange protagonist, and get to learn everything about him. A lot of his family is dead. He has a heart condition. He's super-duper awkward. His English is not so good. We follow him all the way up to the moment that he makes his first real decision. He decides to buy a house, and that's where things get tricky.
Act II
Sorry, No Home for You
Act II is all about the worst possible thing happening, and that's exactly what happens here. Pnin finally has a party where people seem to get along, he's building a space for himself in America, he wants to have a home so that he's not a vagrant anymore. And then it all comes crashing down. Dr. Hagen lets Pnin know that he's fired. It can't get any worse than that.
Act III
Pnin 2.0
This is where things get super weird. The narrator, VN, basically kicks Pnin out of his own story. Suddenly, his whole life story is being retold through this guy's eyes. It's a little creepy.
The whole story ends with this creepster basically taking over Pnin's life. VN takes his job at Waindell and Pnin drives away.