Casey Watson is back, doing the job she does best - rolling up her sleeves and fostering the children who, on first meeting, seem like hopeless cases. But when she meets Miller and discovers the truth about his disturbing childhood, even Casey begins to doubt if this child will ever be able to accept love. Found naked and alone on a railway track, Miller was just five when he was first admitted into the care system. 

After taking a few weeks off work, Casey is presented with a new foster child: 14-year-old Elise, whose Mum left her at just five years old. At first, she’s no trouble at all, that is until she falsely accuses another carer, Jan, of acting inappropriately towards her. It turns out this isn’t the first lie Elise has told—her previous carer was constantly following up allegations Elise had made of people bullying her, trying to have sex with her or hurting her physically. 

Damian is just seven when he is taken in by foster carer Cathy Glass. His mother, Rachel, loves her three young children dearly, but she is vulnerable, naïve and unable to cope on her own. Cathy sets about helping Damian overcome his eating issues, with the hope that he will eventually return home. But when Rachel’s new boyfriend, Troy, arrives on the scene, Cathy becomes deeply concerned. She soon realises that Damian and his siblings are in great danger.

It's late on Friday night when Casey's mobile starts to ring. She is expecting it to be her daughter, Riley. But it isn't Riley. It's a woman from the Emergency Duty Team. So begins Casey and Mike's latest fostering challenge - a 15-year-old girl called Keeley who's run away from her long-term foster home 25 miles away.

Harley, 13, has been sectioned under the mental health act after attempting suicide. She was spotted climbing the railings on a footbridge that crossed a busy motorway and pulled to safety by a member of the public. After six weeks in hospital, social services are looking for a short-term placement so she can be kept safe while family therapy takes place. Harley has a family - a widowed mother and an older sister, Milly, who left home with her long-term boyfriend just over a year ago. 

It's the night before Christmas when Casey and Mike get the call. A 12-year-old girl, stuck between a rock and a hard place. Her father is on a ventilator, fighting for his life, while her mother is currently on remand in prison. Despite claiming she attacked him in self-defence, she's been charged with his attempted murder. The girl is called Bella, and she's refusing to say anything. The trouble is that she is also the only witness....

A 5-year-old boy, Ethan, is brought to Casey in the middle of the night after the sudden death of his young mother after a drug overdose. Estranged from her parents, Ethan’s mum had been abused by her ex-partner, and began taking drugs to cope. Ethan is obviously lost and bewildered, and regularly wakes up screaming for his mum in the night. He begins to lash out at other kids at school and his behaviour becomes more volatile. 

Brought to Casey as a short-term emergency placement, 14-year-old Adrianna arrives with nothing but her gratitude. Having turned herself in to a social services office some 100 miles away, she has no possessions, no English and, apparently, no history - not that she's willing to share, anyway. She is a beautiful young Polish girl, with the bearing of a ballerina, but is terrified, malnourished and unwell.

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.

Three siblings arrive at Maggie's door after being taken into care. Teachers of eight-year-old Bobby spotted bruises while he was getting changed for PE and his dad, Lee, and stepmother, Brianna, have been uncooperative and hostile to Social Services. While they investigate, Bobby, as well as Brianna's daughters, Melodie and Poppy, are all placed in Maggie's care. But as the children settle in, a thought won't let Maggie go. While Melodie and Poppy are clean, well-fed and immaculately dressed, Bobby is pale, severely underweight and crawling with lice.

The Watsons are no strangers to sibling placements, but when Casey takes the call from her supervising social worker one frosty January morning, she can instantly tell from the tone of her colleague’s voice that there’s a complicated case ahead. And she’s right. A four-day-old baby boy called Tommy - born in prison - plus his four-year-old half-brother, the lively Seth. A month later, the very moment she gets out of prison, the boys’ mother - a 19-year-old called Jenna - also follows.

Six-year-old Amelie lives with her mother, Kelly, who suffers from bipolar disorder. After Kelly attempts to burn down their family house, it becomes clear that her daughter is in grave danger. Amelie is quickly taken into care. When she arrives with foster carer Casey Watson, Amelie acts much younger than her age. Casey must get to the root of Amelie’s behaviour, while doing what she can to keep the family together. Will Amelie ever find the safety of home?

Casey's Unit is, as ever, full of troubled, disaffected pupils, and new arrival Leo is something of a conundrum. Thirteen-year-old Leo isn't a bad lad - in fact he's generally polite and helpful, but he's in danger of permanent exclusion for repeatedly absconding and unauthorised absences. Despite letters being sent home regularly, his mother never turns up for any appointments, and when the school calls home she always seems to have an excuse.

Lara was seven when her birth mother died from a drug overdose. With no extended family to look after her, she was put into foster care. The care system failed Lara and now she is failing her son. Lara and her one-year-old son, Arthur, are brought to experienced foster carer, Cathy Glass, by their social worker. Lara has fled an abusive relationship and Arthur has suspected non-accidental injuries. Cathy must monitor Lara whenever she is with her son, day and night. She cannot let them out of her sight for a minute.

Angie, 6, and sister Polly, 4, are utterly distraught when they arrive to stay with foster carer Cathy Glass. Their older half-sister Ashleigh has accused their father of rape, and the two young sisters have been removed from home to keep them safe. Cathy tries to comfort the girls, but they are inconsolable. They just want their mummy and daddy, who they love dearly. The girls appear to have been well looked after, but as they settle and start to talk of life at home, it becomes clear something is badly wrong.