Fallen / Karin Slaughter.

Enhanced descriptions from Syndetics:

There's no police training stronger than a cop's instinct. Faith Mitchell's mother isn't answering her phone. Her front door is open. There's a bloodstain above the knob. Her infant daughter is hidden in a shed behind the house. All that the Georgia Bureau of Investigation taught Faith Mitchell goes out the window when she charges into her mother's house, gun drawn. She sees a man dead in the laundry room. She sees a hostage situation in the bedroom. What she doesn't see is her mother ... When the hostage situation turns deadly, Faith is left with too many questions, not enough answers. To find her mother, she'll need the help of her partner, Will Trent, and they'll both need the help of trauma doctor Sara Linton. But Faith isn't just a cop anymore - she's a witness. She's also a suspect. Faith will have to go up against the people she respects the most in order to find her mother and bring the truth to light - or bury it forever.