This essay reconsiders the career of the most famous of Elizabethan false prophets, William Hacket, the illiterate pseudo-messiah who, together with two gentleman disciples, plotted a civil and ecclesiastical coup, and was executed for treason in July 1591. It explores the significance of autonomous lay activity on the fringes of the mainstream puritan movement, demonstrating links between the dissident trio and key clerical figures who later prudently disowned them. Closer inspection of Hacket's exploits sheds fresh light on the relationship between experimental Calvinist piety and the religious and magical culture of the unlettered rural laity – a relationship still widely presented as bitterly adversarial. Relocated in the context of contemporary attitudes to prophecy and insanity, the episode illuminates the eclecticism of early modern belief and the manner in which medical and theological explanations for bizarre behaviour comfortably coexisted and mingled. Variously labelled a witch, visionary, and raving lunatic, Hacket's case reveals the extent to which such roles, diagnoses, and stereotypes are socially, culturally, and politically shaped and conditioned. In exploiting the incident to discredit Presbyterian activism within the Church of England, leading conformist polemicists anticipated the main thrust of the campaign against religious ‘enthusiasm’ mounted by Anglican elites in the Interregnum, Restoration, and early Enlightenment.