Michael Thompson is a counsellor to some of the most disaffected and challenging teenagers in South London, with pupils ranging from gang members, special needs, migrants and refugees from war-torn countries. It is when he is lured by undercover detectives, from a specialist gang unit, to become a registered informant and spy on his own students, that Michael quickly finds himself in extreme danger and hostile territory. When Michael's father, Edward, a former secret intelligence officer, learns of his son's distress, he sets out to track down Michael with skills he never believed he would have to use again.