Terry Pratchett's Discworld is a post-structuralist landscape where stories are real and magic is a mediating force between reality and representation. Pratchett's Discworld novels possess a strong undercurrent of the recognition of the power of words and the ways in which stories or representations threaten reality. This article examines Wyrd Sisters as a work of metafiction, that is, a work that acknowledges its existence as a representational text and experiments with the idea of "representationality." Wyrd Sisters takes three witches of the Discworld and places them in Shakespeare's Macbeth. The novel's parodic relationship with its hypotext highlights its existence as a work of fiction and, furthermore, draws upon the Shakespearean mise-en-abyme to illuminate the power of representation as a form of magic which has the power to transform, alter, and replace reality. By exposing the artifice of representation, metafiction issues a challenge to the ontological distinction between fiction and reality: by exposing the ways in which texts are constructed by language, the linguistic construction of reality is manifest. By implication, the existence of a verisimilar reality independent of subjective representation is challenged.