Harlem Summer by Walter Dean Myers

Sixteen year old Mark Purvis is an aspiring sax player, who had rather be jamming with his band than finding a summer job, the request of his parents, which prevails. As an assistant at The Crisis, a magazine for the 'New Negro,' Mark rubs shoulders with Langston Hughes and Countee Cullen, and he is invited to a party at Alfred Knopf's place. Mark's making money, but not enough, and when piano player fats Waller entices him and his buddies to make some fast cash, Mark finds himself crossing gangster Dutch Schultz.