Even before James I’s death in 1625, rumours spread that he was being poisoned by a court favourite, the Duke of Buckingham, who had been cultivating the heir to the throne. Historians have long dismissed the charge, but in a detailed reassessment of contemporary sources the authors trace how this scandalous claim was widely published, believed and debated in Britain and beyond. They also examine how it both reflected and shaped political conflicts that would eventually lead to civil war.