Whatever Doesn't Kill You - An Emma Howe and Billie August Mystery, #2

Single mother Billie August is frustrated with her boss and sleuthing mentor, the gruff, perpetually dissatisfied Emma Howe. So far, their relationship has been a personal and professional disaster. To top it off, Billie seems like the only person in town who thinks mentally disabled Gavin Riddock, accused of killing his only friend, might not be guilty, but her inability to turn up any hard evidence could cost Gavin everything.
Now, illness at home and dead ends at work have frayed Billie's nerves. The last thing she needs is to come across Emma Howe in the warpath. Meanwhile, Emma's search for one girl's real mother is being foiled at every turn by the lies and misdirection of the girl's foster mother. When new clues suggest the case may have something to do with Gavin Riddock, seasoned Emma will have to learn to trust her young assistant, and together, mentor and protege must unravel the layers of posh Marin society to uncover the startling truth.