On 19 July 1591, three puritans created a street disturbance in London. They were intending to inaugurate the reign of one of them as the new king of Europe and initiate the transformation of the Church of England to presbyterianism. Some presbyterians hastily dismissed their actions as madness, and historians have tended to agree. The episode is famous, but there has never been a re-creation of the conspiracy’s gestation. The conspiracy grew out of the larger context of Elizabethan presbyterianism, and its formative period strikingly foregrounds the alienation and desperate apocalyptic expectations of that movement at the turn of the 1590s. The conspiracy’s gradual dissolution from passingly plausible eccentricity into sheer delusion can be seen as the presbyterian movement’s mad swan song—insanity as the measurement of the collapse of a viable politics.