has lived on the same London estate for decades. Lately she's become friendly with the little girl next door, who is often left alone for hours at a time while her mum is at work. They have a system. When gets home from school to the empty flat, she knocks on the wall three times. Knock, knock, knock. I'm home safe and sound. But one day Mina's knock doesn't come. Kath raises the alarm, and the police begin the search. Kath was the only person looking out for Mina—now she might be the only one who can bring her home.
