As we know from the other chapters contained in this volume, the De XII abusiuis saeculi and its concentration on the term ‘abuse’ had wide dissemination in the medieval world well beyond the period of its initial composition. The present chapter highlights one such example of this pervasive interest in abuse located in the text of a unique (to the point of exceedingly odd) anonymous Anglo-Norman pseudo-legal treatise entitled the Speculum justiciariorum (usually translated as The Mirror of Justices). By my count, the word abusion shows up 175 times in this volume. Indeed, its fifth and final book is called ‘De Abusions’. Modern scholars—even those who have deemed it worthy of study—commonly treat the Speculum justiciariorum as an idiosyncratic, if not sui generis, book; the adjective frequently employed to describe it is ‘curious’. Although it evidently dates to between 1285 and 1289, its authorship remains in dispute and may never be established with confidence. One aspect of the Speculum justiciariorum that renders it so problematic is its defiance of clear classification. On the surface, it appears to be a version of the common law compendium genre typical of medieval England, comparable to Glanville, ‘Bracton’ and Fleta. Its author clearly knew and relied upon the Bractonian De legibus et consuetudinibus Angliae. As I have argued elsewhere, however, I believe that we ought to count it as a variant of the speculum principum genera. Although the Speculum justiciariorum is no conventional ‘mirror’, it can reasonably be described as a hybrid, a deconstruction and recomposition of medieval English legal theory and practice through the filter of speculum principum conventions.