This article reads Kim de l'Horizon's award-winning novel Blutbuch (2022) as a contribution to the epistemology of gender. Amid philosophical debates about internality and externality in the construction of gender, about the feasibility of gender identity as a coherent concept, about gender feels and gender as process, de l'Horizon's novel offers something else: it shows the foolishness of attempting an etiology of gender and the compulsion to attempt one anyway. Instead of setting the ultimate knowability of gender aside, the typical move of today's gender theory, Blutbuch dwells within this impasse. In the novel, I argue, gender appears simultaneously as an empty signifier and an essential aspect of the self.