At the heart of the book is Mordred, King Arthur's incestuous son, shown by Guerin to be an integral part of the Arthurian tradition from the very beginning. Mordred is seen as the tangible proof of the king's sin, committed in all innocence in his youth but resulting in a living incarnation of evil who will kill his father on Salisbury Plain, putting an end to the Arthurian world. But in the early stages of Arthurian romance, because this story cannot be told without the death of Arthur, it cannot be told at all, for Arthur's existence is the necessary condition of the genre: the story of his death would entail authorial suicide and the impossibility of further literary creation. Guerin argues that the authors of the texts examined in this study - Chretien de Troyes's Le Chevalier de la Charrete and Le Conte du Graal and the anonymous Middle English Sir Gawain and the Green Knight - deliberately use the medieval reader's extra-textual knowledge of the Mordred story to create a second level of reading: behind Lancelot, Perceval, and Gawain is the shadowy figure of Mordred (never explicitly mentioned), and the modern reader must learn to see this shadow in order fully to appreciate the authors' purpose. Taking into account this hidden framework not only sheds a surprising new light on these texts, it also gives a convincing solution to the much-discussed question of why Chretien left two of his romances, Le Chevalier de la Charrete and Le Conte du Graal, unfinished. The first chapter, which deals with Arthurian tragedy in the thirteenth century Prose Cycle, is particularly timely as it coincides with the publication of the first English translation of the cycle, to which Guerin's study serves as an excellent introduction.