In 1988 IRA terrorist Sean O'Callaghan walked into a police station and gave himself up. Sentenced to 539 years' imprisonment for IRA crimes including two murders and many terrorist attacks, O'Callaghan served six of those years before being released by royal prerogative. The reason? For the previous sixteen years O'Callaghan had been the most highly placed informer within the ranks of the IRA and had fed the Irish Garda with countless pieces of invaluable information. He prevented the assassination of the Prince and Princess of Wales at a London theatre; he sabotaged operations, explained strategy and caused the arrests of many IRA members. He has done more than any individual to unlock the code of silence which governs the IRA's members, and in effect made it possible to fight the war against the terrorists. The Informer is the story of a courageous life lived under the constant threat of discovery and its fatal consequences. It is the story of a very modern hero, who is not without sin but who has done and is doing everything in his power, and at whatever personal cost, to atone for the past.