All right, let's break down this sob story. Professor Timofey Pnin (yes, that's Timofey, not Timothy) is a 52-year-old Russian émigré teaching at (made-up) Waindell College. When we meet him, he's on the wrong bus for an event that he's speaking at, and ends up being hours late.
He gets there eventually, but along the way we learn a lot about him. We get the idea that this mix-up is not an isolated incident for Pnin, he's not much of a professor, he's pretty bad at speaking English, he has some kind of heart condition, and he's pretty weird overall. So whoop-de-doo: that's the basic setup for the rest of this novel.
By the way, Pnin is basically a wandering vagrant. When we meet him, he's living with some folks named the Clements, who have a spare room because their daughter Isabel has just gotten married. They don't get along at first, but eventually the three of them develop some kind of odd friendly relationship.
That's when Pnin gets a letter from his ex-wife, Dr. Liza Wind. She left him a long time ago, but now she suddenly wants back into his life. Yeah, we'd be suspicious too, but Pnin is kind of ecstatic about it. He looks forward to the day she's supposed to visit with anticipation. But it doesn't turn out to be exactly what he expected.
Liza appears, insults Pnin and his new lodgings, and then finally tells him what she wants. Money. For the child that she tried to pass off as Pnin's when the two of them were coming to America. He's never so much as met the kid, but now that Liza's getting divorced she needs some more money to take care of him. The whole thing leaves Pnin heartbroken.
Later, there is some more excitement in Pnin's life. It turns out somebody recalls his library book, and Pnin is not very happy about it. Like we said, huge excitement. Anyway, he accuses the only other Russian on the faculty of wanting it, but the guy totally denies it. Then Pnin goes to the library, only to find out that the person who wanted his library book was himself!
After all of that, Pnin heads home. He reads a Russian book and snuggles into bed only to be woken up a few hours later. Like some kind of bad dream, Isabel has come home and it looks like Pnin is going to need a new place to stay.
Fast forward: Pnin has a new room. More news: Victor, Liza's son, wants to meet with Pnin. The kid hates his parents (the ones he lives with) so he imagines Pnin (not his parent) as some kind of scholarly gentleman. Pnin on the other hand, is just excited to meet his "son."
After Pnin meticulously prepares the room where Victor will stay, the two of them meet, a day later than they'd originally planned. Pnin obviously thought this 14-year-old boy was five years old or something. It's awkward. After a few moments of not really knowing what to talk about, they go to sleep.
Fast forward again, and it's summer. Victor is gone, and Pnin is going to hang out with some of his friends. Didn't think he had friends, did you? Actually, this is the only part of the novel that seems to portray Pnin in a positive light.
All is going well, and Pnin is actually winning a croquet match when he gets a heart attack, or maybe it's a seizure. Nabokov doesn't tell us. Anyway, that makes him remember basically the worst thing that has ever happened in his life. And it's no joke: the murder of his first love, Mira, by Nazis in a concentration camp. This is definitely the saddest part of the whole novel. And right when he was about to give a croquet beat-down!
Back to school, and more bad news for Pnin. Dr. Hagen, who's in charge, is leaving the University, which means that someone else will take over his position. The only problem with that is everyone else hates Pnin. So basically that means he'll be fired by the end of the year.
But Pnin, of course, has no idea this is happening and assumes that he'll get tenure soon. He's so happy about it that he even decides to buy a house and throw a housewarming party. It's actually a nice party, and everyone enjoys themselves. At least until Dr. Hagen arrives.
Then Pnin learns the bad news. He's fired.
The last chapter of the novel is dedicated to the kind of weird memories of the narrator. He insists that he has met Pnin several times, but Pnin denies it all. If you look closely, you'll notice there are a lot of historical discrepancies. But the point is, Pnin is being fired and he's going to be replaced by this narrator guy.
The last thing we see of Pnin is his dinky car riding off into the sunset.