Edward Sexby was a figure active during England's Civil War and Interregnum (1642-1660). He is best remembered today for some populist assertions and heated exchanges with Oliver Cromwell during those discussions in parliament's New Model Army on the constitution and future of England known as the Putney Debates (1647), and as the most probable author of Killing Noe Murder (1657), a pamphlet providing learned justifications for Cromwell's assassination in response to his increasingly monarchical Protectorate (1653-1658). Upon a Dangerous Design contextualizes Killing Noe Murder by providing a clearer picture both of Sexby's public life and his relationship with Oliver Cromwell. It considers Sexby roles as a representative for the rank and file of the New Model Army, speaker in the Putney Debates, state servant for the English Republic or `Commonwealth' (1649-1653), and conspirator against the Protectorate and life of Oliver Cromwell. Though focused on a single, extraordinary figure, this study illuminates broader themes of interest to students of political culture. Sexby's public life demonstrates how social and educational barriers separating political groups were permeable and how radical thought and action were intertwined.