This one should be fun: turn-of-the-century detectives in San Francisco. The Spook Lights Affair by Marcia Muller and Bill Pronzini:

In 1895 San Francisco young debutantes don’t commit suicide at festive parties, particularly not under the eye of Sabina Carpenter.  But Virginia St. Ives evidently did, leaping from a foggy parapet in a shimmer of ghostly light. The seemingly impossible disappearance of her body creates an even more serious problem for the firm of Carpenter and Quincannon, Professional Detective Services.

Sabina hadn’t wanted to take the assignment, but her partner John Quincannon insisted it would serve as entrée to the city’s ultra rich and powerful. That means money, and Quincannon loves the almighty dollar. Which is why he is hunting the bandit who robbed the Wells, Fargo office of $35,000.

Working their separate cases (while Sabina holds John off with one light hand), the detectives give readers a tour of The City the way it was.  From the infamous Barbary Coast to the expensive Tenderloin gaming houses and brothels frequented by wealthy men, Quincannon follows a danger-laden trail to unmask the murderous perpetrators of the Wells, Fargo robbery. Meanwhile, Sabina works her wiles on friends and relatives of the vanished debutante until the pieces of her puzzle start falling into place. But it’s an oddly disguised gent appearing out of nowhere who provides the final clue to both cases—the shrewd “crackbrain” who believes himself to be Sherlock Holmes.

Fans of Marcia’s Muller’s bestselling Sharon McCone novels and Bill Pronzini’s Nameless Detective series will applaud The Spook Lights Affairand future exploits from the annals of Carpenter and Quincannon, Professional Detective Services.