The Irish Republican Army's Chief of Staff, Charlie Kerins, is executed by de Valera's Free State government following a tip-off. Sinéad O'Grady, a young and inexperienced Volunteer serving in the IRA during Ireland's Emergency period throughout World War Two is tasked with finding the informer and with assisting a German diplomat in organising an arms drop in rural Kerry. But with a traitor in the ranks, British Intelligence and de Valera's Gardai on her heels, falling in love has got to be a distraction. As an assassination campaign begins, mistrust deepens and Sinéad's life and that of those she loves hang by a thread.