It's February 2019 and experienced foster carer Rosie Lewis has joined Mockingbird, a new fostering scheme designed to help families stay together. After her first week in post, the foster carer takes a call from a social worker in the Child Protection Team - Bonnie, mother of four children, has been sectioned under the Mental Health Act. Her mother, Julie, volunteers to care for her grandchildren, but social workers insist on providing outside support. Julie seems warm and bubbly, looking after her grandchildren with love and care. But then Rosie notices nine-year-old Caitlin, who is lethargic and withdrawn; the child barely lifts her head when Julie and Rosie visit. Rosie senses something's wrong but can't quite get to the bottom of it. As the weeks pass and Rosie gets to know all the grandchildren - Caitlin, Bartley, Ethan and Alfie - she spends more time in the company of Julie, and her husband, Ryan. Moody and distrustful, Ryan has a broken nose and dozens of scars. Rosie begins to wonder what exactly it was that caused the children's mother's downward mental spiral. Could it be that the family have a secret she's not aware of?