If Epitaph for a Loser had been published by in the '50s, it would have been advertised as being "in the Spillane vein" because it's about a private-eye with a .45, and there's some heavy-duty violence in it. It's set in Florida, and I detect a little John D. MacDonald influence, too. Broder's an ex-cop who's doing okay in the p. i. game, not getting rich but getting by. One night his former brother-in-law shows up with a story that Broder doesn't think is quite right. He needs to disappear, he says, because of his gambling debts. Broder gives him some cash, and the guy leaves. Soon his body's found, and Broder thinks the cops have closed the books on the murder too quickly. So does Broder's ex-wife, who hires him to look into things.
As you can guess, there are a lot of people who don't want the investigation to continue, including a bent cop, his Broder's ex-wife's new husband, and a bunch of mobsters. Broder, in the way that fictional p. i.'s have, is undeterred, even when he's savagely beaten and tortured.
You might be way ahead of Broder on the way to the final twist in the tale, but Doyle tells it all well, and Broder's a fine first-person narrator. If you're in the mood for a p. i. story like they don't write anymore, this is a good one.