When Margot goes in search of her birth mother for the first time, she meets her aunt, Nikki, instead. Margot learns that her mother, Susan, was a sex worker murdered soon after Margot's adoption. To this day, Susan's killer has never been found. Nikki asks Margot for help. She has received threatening and haunting letters from the murderer, for decades. She is determined to find him, but she can't do it alone.