This is a fairly standard entry in the Donald Lam/Bertha Cool series. It begins when a man appears in the detectives' offices and asks them to locate a man named Karl that he met in Paris several years earlier. He can't remember the Karl's last name but remembers that he was on his honeymoon with his bride, Elizabeth, and that he came from Citrus Grove, a small town in California. The client, John Ditttmar Ansel, claims to be a writer and says that Karl gave him a terrific idea for a book. Before he writes the book, he'd like to locate Karl and get his permission to use the story.
As usual, Bertha falls for the client's story and sees the chance to make some easy money. And, also as usual, both Donald and the reader know that the story is ridiculous and that Ansel has some other, darker, motive for trying to find good old Karl.
It takes Donald only a few hours to establish that the new client has never written a book or a story that's appeared in any magazine and to also identify Karl as Karl Carver Endicott, the heir to a large fortune. Donald also discovers that Karl Endicott was murdered in Citrus Grove several years ago, at just about the time Ansel claims to have met him in Paris. The crime remains unsolved and the principal suspect, described by a cabbie who drove the suspect to the victim's house, very closely resembles John Dittmar Ansel.
Donald is thus almost immediately up to his neck in another complicated mystery filled with cops who want him off the case and several sexy women who want other things of him. As always, it will take some pretty fancy footwork for Donald to stay ahead of the police while juggling the women and attempting to solve the crime. The solution to this case is one of the more interesting in the series, and in all, Beware the Curves is another entertaining entry in it.