The complex dynamics of space and time present in some of the stories of Adolfo Bioy Casares have their roots in the interstitial that separates the genres of fantasy and neo-fantasy, and most of all in the suggestion of ontological ideas and doubts that characterise the latter. Deeply rooted in the unknown land of a reality that is full of doubts, the literature of Bioy Casares seeks to restore, through the multiple games of fiction, the perception and perceptions of a continuous changes that end with generating parallel worlds. The neo-fantastic passes the crucial limit of traditional fantasy, the stable and certain dichotomy between the real and the imaginary, and to do this it relies on the fragile foundations of a reality in full process of deconstruction. The centre of immateriality in which are born the sinuous spatio-temporal bifurcations that structure stories like “La Trama Celeste” of Bioy Cesares or “El jardín de senderos que se bifurcan” (1941) of Jorge Luis Borges has its origins in an instability that is inscribed in the real. Therefore, when during a period of crisis the rules which govern a culture become shrouded in doubts and demonstrate their false transparency, the neo-fantastic can transform itself into a fundamental tool for describing the crucial nature of the destabilisation taking place: it converts itself into a mimetic process at the structural level.