Jenny Hilborne. No Alibi (2011) [e-book]
Publishers description: Isabelle Kingsley didnt think her husband would ever cheat. Her husband didnt think she would ever find out. Now he is missing, and his mistress is dead. Suspected of killing her, Isabelle turns to her best friend, only to discover another betrayal. Is there no one she can trust? [San Francisco] homicide cop, John Doucette, is on the case. Something about Isabelle unnerves him. Could she be innocent? If she is, how did the murder weapon come to be in her possession? Someone from her past connects them; someone that Doucette does not want to face. Doucette must set aside his personal feelings and fears to work through the tangled web of deceit before the case goes cold and a killer goes free.
Setting: San Francisco