The photo on the card shows a teenager who was found murdered a year ago near a girls' boarding school in a suburb of Dublin. The caption reads: I know who killed him.

Detective Stephen Moran had been waiting for a long time for the opportunity to step through the door of the Homicide Division, and his wish comes true when sixteen-year-old Holly Mackey brings him this card. She found it posted on the Place of Secrets, a board where the girls of St. Kilda's private school can anonymously post their secrets. Someone used it to rekindle the investigation into Chris Harper's murder. Stephen will team up with the tough detective Antoinette Conway to find the solution.
All the clues lead them to Holly's clique and their rivals' clique. With every step they take, the pressure mounts. The world of these teenage girls will prove to be far more dangerous than the two detectives ever imagined...