Twenty years ago, Jackie Galloway was a senior cop with a bad reputation. But after crossing the wrong people, his career was ruined. He eked out his last days succumbing to dementia on Scotland's Black Isle, supported by his long-suffering wife, Bridie. When he’s found dead, the police assume it’s an accident—until Bridie reveals that he’s been receiving mysterious letters containing only the phrase: “NOT FORGOTTEN. NOT FORGIVEN.”