What happens to children's souls when they die? They are recruited to become Guardian Angels... And fight the Fallen. Cai Smith is a guardian angel who watches over teenagers at a mental health facility with the highest suicide rate in England. After one too many deaths, Cai returns in mortal form as a teacher at the hospital school. His mission: to figure out what's behind the suicides and stop it. Grace Gallagher is a clinical psychologist who is inexplicably drawn to the new teacher. When she first meets Cai, she misreads his terseness as rudeness. What she doesn't realise is that he has recognised her as someone he knew before he died. Together they become embroiled in a battle between Angels and the Fallen, fighting to save patients' lives and their own, all the while wondering if there are second chances at love-especially when one of them is dead.