More and more of the better crime novels these days defy the confines of “genre fiction”. Michael Nath’s The Treatment (riverrun, £20; Tablet price £18), with its cast of more than 100, and its ­frightening, hilarious portrait of contempor­ary London, criminal and otherwise, invokes Dickens in its early stages (two characters discuss Our Mutual Friend) and it is in all the best senses Dickensian. The starting point is a hideous racist murder, clearly based on that of Stephen Lawrence. The story is about how a group of people, for a number of reasons, hunt out one of the racist hoodlums who managed to escape arrest for the killing. In the process, with many a suspense-filled incident, we meet a gallery of grotesque yet entirely believable characters, and overhear some of the most interesting dialogue I’ve read in years. The narrator, Carl Hyatt, a ­middle-aged reporter on a dud newspaper, married to a science teacher, befriends a male “sex worker”, Donna Juan, who has taken bloody revenge for homophobic bullying in his youth.