The Crooked Street by Brian Freeman
The third in the Frost Series- San Francisco homicide detective Frost Easton hadn’t seen his estranged friend Denny in years. Not until he dies in Frost’s arms uttering a final inexplicable word: Lombard. Denny appears to be the latest victim in a string of murders linked by a distinctive clue: the painting of a spiraled snake near the crime scenes. Is it the work of a serial killer? Or is Denny’s death more twisted and personal?
To find the answer, Frost reaches into a nest of vipers—San Francisco’s shady elite—where the whispered name of Lombard is just one secret. Now, drawn into a cat-and-mouse game with an enemy who knows his every move, Frost finds there is no one he can trust. And somewhere down the crooked streets of the city, Frost’s cunning adversary is coiled and ready to strike again. —Goodreads