A Garda sergeant is found beheaded with an Irish tin whistle sticking out of his neck. He was due to give evidence at a major inquiry into police corruption. The murder sends a clear message to any future whistleblowers: silence is safe.
The corruption inquiry hinges on the arrest of one of Cork's most dangerous drug dealers. There was enough evidence to convict him, but instead he walked free. The arresting officer was DCI Katie Maguire and she's determined to expose the truth.
But when another officer is found murdered in the exact same way, Katie soon finds that people would rather keep a dirty secret than lose their heads.