When Bill Rivers put a copy of his debut novel, Last Summer Boys, in my hand earlier this summer, he didn’t tell me it came with blurbs from former Secretary of Defense James Mattis, for whom he had been a speechwriter, and Archbishop Charles Chaput of Philadelphia. We met in order to do something of an interview: I wanted to get to know a young writer who seemed unusually bashful in an era of self-promotion; indeed, Bill was more inclined to hide his résumé than brag.