In the first couple of paragraphs, a guy has plastic surgery to make himself look like Bogart, changes his name to Sam Marlow, buys a '39 Plymouth, and opens a detective agency. It takes a while for the clients to start arriving, but when they do, the fun begins.
And it's a lot of fun, for sure. Marlow has the Bogart patter down pat, and Fenady has the L. A. scene down the same way. You're probably thinking you saw the movie version, and that's the poster on the left. I liked the movie, too, but (as is so often the case) I liked the book a little better. Robert Sacchi had a nice run doing Bogart stuff (you can see him in commercials from the era). You might want to check Netflix for the movie, but get the book first.