Based on the true story of one man's fight against one of the greatest miscarriages of justice in British legal history. Starting more than 20 years ago, the Post Office wrongly dismissed, harassed, and prosecuted hundreds of innocent sub-postmasters for theft, fraud, and false accounting. Sub Postmasters were told they were the only ones to report a problem with a new computer system called Horizon. When Alan Bates was fired, he refused to accept the Post Office blame. He found and brought together a group of other isolated and wrongly accused victims to form the Justice for Sub Postmasters Alliance. Alan Bates and his friends exposed a shocking scandal at the heart of the Post Office, a government-owned and much-loved national institution.