The Barbarous Coast by Ross Macdonald
If you haven't encountered Lew Archer yet, think Philip Marlowe with a less terse and more poetic turn of phrase. Ross Macdonald's private eye also works in California and the 1956 novel The Barbarous Coast sees him taking on a case in Malibu that starts out as a simple request for a bodyguard. It's quickly replaced by the search for a naive Canadian sports reporter's errant young wife, believed to have returned to her Californian roots. Even that doesn't remain Archer's focus for long, and he follows a trail to the filthy underbelly of Hollywood, where the glamour cracks apart to reveal blackmail and murder. Dreams turn rotten with age, and cops turn rotten with money, and all the while Lew Archer does his best to remain unsullied and serve up justice when even the good guys are asking what's the point.
One thing I particularly liked about The Barbarous Coast was the almost total absence of police, except as shadowy figures in the past, or offstage characters who Archer hands evidence to. Until this felt so refreshing, I hadn't noticed how often private detectives run up against obstructive policemen, or work around the activities of the police department, trying to stay one step ahead. Because the police aren't interested in the justice Archer is looking for, he has free rein and over a couple of very long days his determination allows him to gather the evidence he needs.
The novel does use a sneaky ploy that, depending how much of a murder mystery purist you are, you may find irritating. However, because I spotted it before Archer did, I didn't feel tricked and I was prepared to forgive his slow realisation on the grounds that he was tired and overworked. With its sad portrayal of love gone sour, and the exploitation of vulnerable people, this is not a light-hearted read but I found it gripping and satisfying, and I'd recommend it to readers of the flawed American dream (F Scott Fitzgerald perhaps?) as well as lovers of classic noir.