This dissertation revisits a set of Middle English romances of the thirteenth and fourteenth century to ask what motivates their forms. In the verse romance Havelok the Dane, readers are given three signs of the dispossessed Havelok's royal heritage: a bright light that shines from his mouth, a birthmark in the shape of a cross on his shoulder, and the entrance of an angel who identifies him as prince of Denmark. Ultimately, however, his subjects recognize his nobility from his face, which resembles that of Birkabeyn, the former king. Why does the romance linger on these elaborately fantasized signs of his heritage when the most effective proof turns out to be the simplest? Any answer that maps narrative onto ideology sidesteps the seething narrative pleasures of such tangents. Such seemingly inconsequential reiteration is common in romance, a genre that reliably rejects ordered causality in favor of prolific repetition and elaboration of crucial narrative moments. From Patricia Parker to Jacques Lacan, critics have long noticed that the episodic forms of romance are characterized by a deferral of closure; romance makes conventional its very rejection of teleology, endorsing a form marked specifically by its meandering, open-ended embrace of possibility. The narrative conventions of romance set themselves purposefully at odds with ideological narrativity, producing a space wherein expansion is privileged over explanation. But what does such radical openness accomplish? My dissertation interrogates the productive capacity of extended moments of integration, literary spaces that narrate the transition between the comprehensible and the strange. Todorov, in a very different literary context, called these moments "the fantastic": hesitations that arbitrate between a familiar world and the unknown. Affect studies, with its emphasis on the way that actors receive and interpret the world, offers a model that resembles Todorov's fantastic on the scale of the body rather than that of the narrative world. I use both concepts as resources to map romance's commitment to dilated interstices between sensual experience and articulable understanding. This dilation, I argue, offers the writers of romance a way to play out political possibilities that rejects allegory and direct narrative causality, dwelling instead in the deliberately artificial space of the narrative's formalizing constructs. Romance is crucially oriented around the moment at which the predictable becomes unpredictable; it focalizes the relation of form to content in a way that offers up a distinct discursive mode. In each of the four chapters of "Fantastic Worlds," I consider a single romance in Middle English as a case and examine how the distention of moments of narrative intensity alienates recognizable cultural forms. Romance interrogates political possibility by setting its own formal expectations, of dilation and delay, at odds with predictable structures-forms of closure, forms of comprehensibility, forms of cultural presumption. The collision between the articulable and the persistently strange offers a new archive for affect theory's attention to literary spaces of intensity and atmospheric contingency. Further, attention to such effects illustrates how romance, typically understood as simple or propagandistic, can in fact produce complex and compelling ethical scenes, crafting a world that allows for-and more importantly, produces-possibilities opposing the determinate, categorical shapes of ideological expectation.