A year ago a boy was found murdered at a girlsʼ boarding school, and the case was never solved. Detective Stephen Moran has been waiting for his chance to join Dublin’s Murder Squad when sixteen-year-old Holly Mackey arrives in his office with a photo of the boy with the caption: “I KNOW WHO KILLED HIM.” Stephen joins with Detective Antoinette Conway to reopen the case—beneath the watchful eye of Holly’s father, fellow detective Frank Mackey.