I should preface this by saying that as 30something adult, I don't seek out "YA" (young adult, aka teen) fiction for my leisure reading. In the case of this book, I didn't realize it was a YA title until I was already hooked, and since I'm a fan of quirky coming-of-age novels, it pretty much fit right into my comfort zone. The story is about recent high-school graduate Colin. A former child prodigy, he is now merely another smart teenager with underdeveloped social skills and a yearning to leave his intellectual mark on the world. With the summer between high school and college to kill, he's also heartbroken because his girlfriend, Katherine, just dumped him. Actually, she's the nineteenth Katherine to sever relations with Colin (hence the title) -- although one of the book's enduring mysteries is how someone as neurotic as Colin manages to have relations with 3, let alone 19 girls, whatever they may be named.
In any event, Colin is fortunate to posses a roly-poly sidekick/best buddy named Hassan, who promptly prescribes a road trip as the cure for his malaise. Couch potato Hassan provides much-needed comic relief with his blunt talk, tough love, and love for bad daytime TV. It's also nice to see an Arab-American character in such a role. The road trip takes them to a small town in Tennessee, where they stumble into jobs and a place to stay for the summer. They also luck into friendship with a cool local girl named Lindsey and spend a good deal of time hanging out with her and her Abercrombie-wearing friends. Meanwhile, Colin is hard at work trying to figure out the variables needed to plug into a mathematical formula which will graph the rise and fall of any relationship. This provides the excuse to learn about the 19 Katherines, although thankfully just enough to help the reader understand how they affected Colin.
As the summer progresses, the story unravels much as one might expect, with the notable exception of an unlikely hookup between Hassan and another character. Lindsey naturally turns out to have hidden depths, and despite the expected heart-warming developments at the end, the story kind of peters out without the closure one might expect. Overall it's a worthwhile read, although it's not a particularly challenging story and Colin is simultaneously too self-pitying and too handy with the ladies to be a truly sympathetic protagonist. Some of Green's stylistic tics work, such as the many footnotes, but the mathematical relationship formula felt kind of gimmicky. Still, this is the second YA novel by Green, and it's definitely enjoyable enough to make me think about seeking out the first.