This paper examines the ambivalences, and tensions of the imperial project encoded in 19^th century botanical codification of poisonous plants in British colonies, through the materiality of alkaloids in Sherlock Holmes stories. I argue that these tales reveal the orientalising gaze of botanical codifications which merged in the case of study of alkaloids with medico-criminal discourse on plants, that grouped indigenous plants, and indigenous people under the canopy of toxicology, constructing the native population as criminal and primitive, thereby giving imperial crimes a clean-chit. I contend that this bundling of forensics and the sociological was damage control of the faltering British self-image in the wake of Britain’s anti-opium movement and atrocities in the Boer war. The Holmes mysteries link phytotoxins to colonies’ cultural practices, thus reattaching criminality to the colonies, to re-institute British selfhood in metropolitan consciousness by creating via the flora of the colonies, a criminal Other. However, I point out that the institutional weight of imperial machinery could not fully contain the unease of Britain’s colonial contact. The anxiety of reverse-colonialism (1857 Sepoy Mutiny), continued to haunt the British psyche, appearing as exotic alkaloids that leave no trace, and can only be deduced by Holmes’ genius. Such that, plant poisons in these tales simultaneously repair British loss of self-prestige, as-well-as, self-subvert it. I study homicidal poisoning tales, “The Adventure of the Devil’s Foot” and “The Sign of the Four,” as stories of revenant, disavowed (thereby spectral, intangible) imperial unease, using Jacques Derrida’s political idea of systemic evils as spectral (Specters of Marx, 1994). The plant-poisons of these tales, I argue, are conceptual tools, revealing spectres (not to be confused with cliched ghosts) of imperial anxieties, disturbing the stability of imperialism’s coerced archiving, gathering us under its revealing spectral shade.