Third Rabe: It's My Funeral by Peter Rabe, 1957, 2014 and 9781933586656 for Stark House omnibus.
Daniel Port is hanging out in Los Angeles. Port has no particular reason to be there but just got into town, bought an MG and is heading to the beach. Being new to town he wonders why a Cadillac seems to be following him. After a swim in the ocean Port is getting some sun when up walks his old "pal" Mnuchkin. Okay, that's not actually his name but I think 'Mnuchkin' is close and they're both sleazy.
Mnuchkin is a crook who worked for Port's boss from the first book. Mnuchkin is persistent - he'll ignore any slight or insult and keep pressing on to get POrt to lend him a hand. Port does not want to get involved with anything Mnuchkin is up to even though Mnuchkin says he is now on the up and up and working as a legitimate talent agent.
But, the help Mnuchkin is asking for is help with a blackmail case. A famous starlet - a Marilyn Monroe or similar stand-in who is now named MarMon - is getting blackmailed over a sex film. Port decides to help out (for some reason I don't recall) and starts getting involved with Mnuchkin, MarMon, and a studio boss's self-important son. Never mind Port's wooing of a local singer and clashing with a Nevada crook also interested in The Singer.
Many things happen. Port drives his tiny MG among all the Cadillacs of Hollywood. Port heads to Nevada to visit The Singer and stumbles upon a blackmail operation that goes after the female celebrities who stay in a casino's performers' suite.
There are some fist fights. A couple car crashes. A few concussions. Backstabbings. Disrupted lovemaking. Weasels. So on. So forth.
Of the three Rabe novels I've read I think this is the best.