Blue City by Ross Macdonald
He was a son who hadn’t known his father very well. It was a town shaken by a grisly murder—his father’s murder. Johnny Weatherly was home from a war and wandering. When he found out that his father had been assassinated on a street corner and that his father’s seductive young wife had inherited a fortune, he started knocking on doors. The doors came open, and Johnny stepped into a world of gamblers, whores, drug-dealers, and blackmailers, a place in which his father had once moved freely. Now Johnny Weatherly was going to solve this murder—by pitting his rage, his courage, and his lost illusions against the brutal underworld that has overtaken his hometown.