This article deals with witchcraft, missionisation, domestic slavery and social life on the emerging colonial ‘frontier’ of Onitsha, Nigeria, during the last years of the nineteenth century. The analysis centres on the confession of an accused witch and former domestic slave in the Waterside area of the town. It uses the document as a springboard for a larger discussion of the intersecting lives of Africans and Europeans in this marginal location at a moment when social relations there were undergoing radical transformation. By addressing such a text, taken down verbatim at the time of the confession, the author argues, we can gain a privileged insight into women's unofficial (and even prohibited) religious practice as well as the everyday lives of persons—notably female domestic slaves—who ordinarily receive little notice in the African colonial record. From Okuwan's confession we also learn something about how the increasing flows of commodities and new forms of colonial authority along this mercantile border were changing (and possibly devaluing) African women's labour as well as their religious power.