Ah, Ross Macdonald. I'm becoming rather fond of him. Good I discovered him. He gives a nice break from re-reading Raymond Chandler endlessly.
This plot is rather convoluted, so I'll only touch on a bit. A rich old lady, Maria Galton, thinks herself to be on the verge of death. Before that happens, she wants to reconnect with her son, and grandson, both of whom disappeared some 20 years previously. The son was a bit of a beatnick, ran off to San Francisco with a young woman he had impregnated and started writing poetry, or something. Whatever, no one has seen hide no hair of him since. So, Mrs. Galton's lawyer, Gordon Sable, hires Lew Archer to find the missing relatives.
Eventually, through a series of coincidences, perhaps intentionally directed ones, Archer finds that the son and grandson lived for a time in a place called Luna Bay, but then disappeared in the night, so to speak. After several rounds of interactions with mobsters and other shady characters, not to mention the knifing of Sable's houseman in front of Sable's unstable young wife, Archer figures out that the, now deceased, houseman also has some ties to Luna Bay.
Then, a young man shows up, claiming to be the missing grandson. He says that he had been living in an orphanage in Ohio, but escaped at 16 or so and found refuge with a professor at the University of Michigan in Ann Arbor, where the young man studied and graduated (I think he got a degree). But, there's a problem. How to prove the young man's story. The orphanage in Ohio had long since burned down, and its records with it. Then too, the young man shows hints of pronunciation and spelling more in keeping with his having been brought up in Canada than in Ohio.
Well, things go on, people die and get beat up. Eventually, Archer figures it all out. Really a quite fun story if you're at all into hard-boiled, noir, detective fiction, i.e. the stuff of Raymond Chandler and old Humphrey Bogart films.