It's 1921, and Liam Mannion is embroiled in the murky world of informers and spies; the IRA has announced a truce, and the British and Irish leaderships are taking their first tentative steps toward signing a treaty. Liam and his fiancee, Kate, are tasked with finding republican rotten apples, some of whom are intent on foiling the fledgling peace talks. For Kate, the Brigade Intelligence Officer, that means asking awkward questions of trusted allies - questions that reveal a traitor. For Liam, it means travelling to London and collaborating with the British police to find a killer. As the search unfolds, a devastating revelation from Liam's past will make the hunt more personal - and deadly - than even he could imagine.