Bye-Bye, Black Sheep by Ayelet Waldman
Juliet Applebaum is a former public defender, currently a private investigator. Her partner, Al Hockey, is a former detective with the LAPD. Juliet has 3 children, and a husband who is a successful screenwriter.
Heavenly, a transvestite, shows up at their office, asking for help investigating the murder of her sister Violetta, a prostitute. The police are ignoring the death, and Heavenly just wants closure for herself and her family. Juliet agrees to investigate, and finds herself hanging out with streetwalkerss and pimps on Figueroa in South Central, a far cry from her home in the Hollywood Hills. It gets to the point where Juliet's husband Peter and Al are so concerned about Juliet's safety that they try to forbid her to go there.
But Juliet survives, and she solves the case, though the identity of the killer is totally unexpected.
I really like this series. Juliet is by no means perfect, she struggles with her weight, and with being a good mother, wife, and PI and somehow manages to stay sane.
Next up: End in Tears by Ruth Rendell