“Free indirect discourse” (FID) is one of the most complex and problematic modes of representing characterological consciousness in literary discourse that gained considerable significance in written storytelling specially in the wake of High Modernism. The present article aims at offering a theoretical synthesis of the most prominent accounts of FID in (English-language) prose narrative fiction within the framework of the classic theory known as the “dual-voice hypothesis.” First, characterological discourse and its constituent elements in narrative fiction are illuminated. Next, the different modes of the narrator’s representation of characterological discourses are discussed separately according to the quadripartite model, which includes direct discourse (DD), indirect discourse (ID), free direct discourse (FDD), and free indirect discourse (FID). Then, in an extensive survey that interweaves structuralist and poststructuralist accounts, the textual markers of FID, as a dual voice, and its functions in narrative fiction are examined. The poetics offered in this paper supports the dual-voice hypothesis, namely that the presence of FID in a narrative often results in “polyvocality,” a state in which different narratorial and characterological discourses co-exist, without one predominating the others. Exploring the relations of this vocal ambiguity to such formalist, structuralist, and poststructuralist concepts as semantic density, defamiliarization, polyphony, intertextuality, différance, and deterritorialization, the study concludes by demonstrating how FID renders the narrative “writerly,” a positively ambiguous text open to various and even conflictual interpretations, and that accordingly it can be deemed an index of the literary and the narrative.