Early on in Triksta, the white, middle-aged British music writer/novelist Nik Cohn admits that he’s racist. To confront his long-ingrained prejudices, Cohn submitted to an unusual cure: In 2000, he dived headfirst into New Orleans’ chaotic hip-hop scene with the goal to become a star-making rap impresario. It didn’t quite happen, but Cohn’s journey through this world of teenage rappers, rickety studios, and crumbling housing projects is a humane and fascinating view of a culture that isn’t widely known. (His chapter on the history of rap, however, is skippable.) Already gone to press when Hurricane Katrina hit, Cohn’s book reads more like a heavyhearted memorial than a celebration.