The photo shows a boy who was found murdered, a year ago, on the grounds of a girls' boarding school in Dublin. The caption says I Know Who Killed Him. Detective Stephen Moran has been waiting to get a foot in the door of Dublin's Murder Squad. One morning, sixteen-year-old Holly Mackey brings him this photo from an anonymous message board at St. Kilda's School. Moran joins forces with Detective Antoinette Conway to find out who and why.