This article examines the relationship between the fin de siglo discourse of occultism and the origins of the fantastic genre in Latin America. Through an analysis of Eduardo Holmberg's 'Nelly' (1896) and Leopoldo Lugones's Las fuerzas extrañas (1906), I argue that these writers inaugurate the fantastic narrative as a means of investigating the mysterious phenomena of the occult sciences — the realm of ghosts and other 'strange forces' — thereby expressing one of the cultural preoccupations of the fin de siglo: the tension between scientific precepts and spiritual beliefs. The ghosts in Holmberg's novella bring in the mystery of spirit manifestations, pointing to the gaps in human knowledge and thereby subverting the hierarchies of truth that divorce science from fiction. Lugones's work, however, goes even further by problematizing the scientific laws of nature in order to create a new hierarchy of knowledge, as he closes Las fuerzas extrañas with an essay that lays out a whole set of occultist laws that purportedly govern reality. Hence, the fin de siglo fantastic sets the stage for a Latin American literary tradition, namely the prominence of literary modes that subvert realism in an attempt to articulate an alternative notion of reality itself.