The mirror of simple souls, written in Old French around 1300 by a beguine named Marguerite Porete, was a mystical dialogue concerning the soul's union with God. Although it was extremely daring and, depending on one's point of view, perhaps heretical, its literary quality and depth of imagination were admired by many contemporary readers. Consequently it was translated into Latin, Middle English and Italian by individuals who did not know that its author had been put to death in Paris because of the Mirror's ‘errors.’

The late-medieval reception went in opposite directions. (Trombley's title, A diabolical voice, misleadingly refers to only one of them.) An example of the Mirror's continued popularity in the fifteenth century is that thirty-six copies of the Latin translation were available to be brought to the Council of Basel. But these copies were brought there to be burned. Whereas an illuminated initial in a fifteenth-century Latin copy displays a monk gazing at the words of the Mirror appreciatively, a critic branded the work as ‘worthless, deceptive, and dangerous’. Obloquy went still further. Another critic fulminated that: ‘Those who say such things should be confounded and ashamed. May death come upon them, and may they descend living into hell . . . their eyes should be dug out and their tongues extracted with a savage hook.’ Although nothing was known of the author, other than the mistaken presumption that ‘he’ was male, hostile readers would have been gratified to learn that ‘he’ was burned to death for heresy in Paris in 1310.

Justine Trombley is not concerned with Marguerite's career or trial. (For that readers should turn to the basic account written by her dissertation supervisor, Sean Field: The beguine, the angel, and the inquisitor: the trials of Marguerite Porete and Guiard of Cressonessart, Notre Dame, In 2012.) Instead, A diabolical voice treats the reception of the Mirror in fifteenth-century Italy. Positive reception is indicated by the existence of many copies located in or near Venice. But Bernardino of Siena and John of Capestrano vilified the work. Trombley offers three substantial chapters that responses to the Mirror found in three hitherto neglected Italian manuscripts. (She excels in locating new sources.) In the first she employs consummate technical skills to treat a mutilated copy of the Mirror in the Bodleian Library, Oxford: ms Laud Latin 46. One might have wondered what could have been gained from this manuscript, because someone who found the Mirror dangerous excised seven pages that comprised nearly the entire work. But the determined Trombley found that ‘there is more to the Mirror here than previously thought’. The opening lines went unscathed because they followed a writing that the owner wished to retain. Additionally, some marginalia can be discerned on stubs from the excised pages, and a previously unnoticed binding error resulted in finding a page that had at its top the last part of the evaluation of the Mirror by the Parisian theologian Godfrey of Fontaines and the concluding sentence of the Mirror itself. Close attention to detail reaps its rewards.

Trombley then pioneers in addressing critiques of the Mirror in ms Vat. Lat. 4953, and University Library, Padova, 1647. The first contains a list of ‘errors’ and theological refutations; the second opposes expressions in the Mirror from the point of view of canon law. (This is substantially new material, well exploited.) Trombley might have done well to have mentioned John Baconthorpe's contemporary denigration of the Mirror as ‘a little book against the clergy’, and she errs in writing ‘William Auvergne’ instead of ‘William of Auvergne’. But she is capable of some nice phrases such as ‘Bernardino, the rock-star Franciscan preacher of his time’, or estimations such as ‘Marguerite should be included just as readily alongside figures like Peter John Olivi as she can alongside Joan of Arc.’ As Jacques Delarun notes in a jacket blurb, ‘this exceptional book does much more than illuminate the reception of the Mirror of simple souls; it goes back to its doctrinal content and illuminates the text itself’. This is one of the most original and searching accounts of the reception of The mirror of simple souls that has been written.