S12, E9: The discovery of a dead 12 year-old floating in a drainage ditch brings, Nikki back in contact with one of her former teachers, Noel Hopkins. During Harry's preliminary examination they find clear signs of abuse. And when the police discover the victim was last seen with another boy, Liam, who is now missing, they fear he may have been abducted. A paedophile ring is suspected; the dead boy's stepfather comes under suspicion, as does Noel - but Nikki can't believe he'd be involved. Then a badly mangled body is found on train tracks near the woods where the boys went missing.