This ambitious and important book is a richly detailed account of the ideas and activities in the early-modern ‘secret state’ and its agencies, spies, informers and intelligencers, under the English Republic and the Cromwellian protectorate. The book investigates the meanings this early-modern Republican state acquired to express itself, by exploring its espionage actions, the moral conundrums, and the philosophical background of secret government in the era. It considers in detail the culture and language of plots, conspiracies, and intrigues and it also exposes how the intelligence activities of the Three Kingdoms began to be situated within early-modern government from the Civil Wars to the rule of Oliver Cromwell. It introduces the reader to some of the personalities who were caught up in this world of espionage, from intelligencers like Thomas Scot and John Thurloe to the men and women who became its secret agents and spies. The book includes stories of activities not just in England, but also in Ireland and Scotland, and it especially investigates intelligence and espionage during the critical periods of the British Civil Wars and the important developments which took place under the English Republic and Oliver Cromwell in the 1650s. The book will appeal to historians, students, teachers, and readers who are fascinated by the secret affairs of intelligence and espionage.