Curiously placed between the realms of science and supernaturalism, the phenomenon of the uncanny double has a distinctive presence in both. Another kind of duality is at issue in the imagined presence of the doppelgänger, as a figure in both physical and mental life. While the phenomenon of the Brocken spectre is one of the era’s most resonant manifestations of an uncanny mirroring of the body, later nineteenth-century developments in clinical psychology began to focus on the sense of an alien presence residing in unknown reaches of the human brain. As they did so, these clinical experiments involved an engagement with the interweave of mental and physiological expression. In Nicholas Royle’s words, the uncanny is associated with ‘a flickering sense (but not conviction) of something supernatural’. Somewhere between the conviction afforded by cognitive processes and the flickering sense intimated by the live wiring of the nervous system, new dimensions of reading and interpretation were opened up. My concern here is to explore how the overlay of scientific and supernaturalist frames is managed in some of the more influential literary and dramatic portrayals of uncanny mimesis. These include evocations of the doppelgänger in works by Thomas De Quincey, James Hogg, and Walter Scott, and in Henry Irving’s theatrical productions. Irving’s interest in the double consciousness of the actor is discussed in relation to psychological theories of dual consciousness, and their exploration in clinical practice with patients diagnosed as hysteric.