Whipping Boy by Allan Kurzweil (2015)

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Subtitled The Forty-Year Search for my Twelve-Year-Old Bully, I loved this book immediately.  

Novelist Allen Kurzweil, who was sent to a Swiss boarding school after his father's untimely death, was bullied by another student. In adulthood, he became obsessed with figuring out what happened to his childhood tormentor. Amazingly, what happened to his bully is so unbelievable that Kurzweil had to make it a nonfiction book--no one would believe it if it was a novel. 

His bully was part of a fraud ring that involved elaborate banking scams, and amazingly eccentric character--one wears a monacle! After a bit of a digression into the details of the fraud case, he returns to the resolution of his emotionally charged quest. And the resolution is really, really satisfying. Great story.