Marguerite Porete is a name recognisable to many medievalists: beguine and mystic, author of the treatise The mirror of simple souls, and sentenced to death as a relapsed heretic in 1310, with the (unsuccessful) command that all copies of her book be destroyed. Less well known is Guiard de Cressonessart, who attempted to defend Marguerite in Paris, was himself then arrested, and during his trial alleged to his inquisitors that he was ‘the Angel of Philadelphia’; that is, performing the office of an angelic figure mentioned in the Apocalypse of St John. On 1 June 1310 Marguerite was burned at the stake. Sean Field has produced the most important, scholarly and detailed study of the case; in terms of the technical details, chronology and historical context his book is the final word on the subject. Field translates the core documents as appendices to the monograph (the monographic element here being about 200 pages, the remainder of the book appendices and notes), and has taken painstaking care in clarifying the precise order of events, clearing the waters which were muddied by nineteenth-century scholarship. Frequently the author looks sideways at other contextual events or potential connections: the important fact, for example, that the trials against the Templars were proceeding at the same time in Paris, with some of the same figures and personnel involved. Field is exceptionally good on details, noting for example the curious fact that a Templar named Matthew of Cressonessart was in Paris, attempting to defend his Order, at the very same time that Guiard was being prosecuted. Two men, from the same small hamlet in northern France, in Paris at the same time, both grappling with the combined power of secular and ecclesiastical authority; nothing more than a coincidence, but strongly resonant none the less. Details such as this illustrate the very great strengths of Field's study: great fidelity to the sources, huge care over details, the patient ability to track down byways and contextual elements. The interpretations and conclusions that he offers are informed by this approach, in that they are careful, cautious and more directed to ‘who, what, when’ than ‘what it all means’ – though he does offer very interesting thoughts on the political context of the prosecutions and their outcomes, and what we should (or should not) make of Marguerite's apparently steadfast silence in the face of inquisitorial questioning. In short, this is a fabulous piece of technical scholarship, and is absolutely required reading for anyone who works on Porete. It is also a very powerful case study for understanding the political context in which a prosecution for heresy is carried out, of great importance therefore for those working on inquisition, heresy and the sharp end of orthodoxy.