Memory in Death by J.D. Robb

Eve Dallas is one tough cop. She's got no problem dealing with a holiday reveler in a red suit who plunges thirty-seven stories and gives new meaning to the term "sidewalk Santa." But when she gets back to the station and Trudy Lombard shows up, it's all Eve can do to hold it together. Instantly, she's plunged back into the past, to the days when she was a vulnerable, traumatized girl - trapped in foster care with the twisted woman who now sits in front of her, smiling.