This paper examines evidentiality and epistemic modality in Quechua narrative discourse from the central highlands of Peru. Huamalíes Quechua falls into the broad Quechua ‘I’ dialect grouping established by Alfredo Torero (1964); evidential usage here can be compared to that of southern Conchucos Quechua as studied by Diane and Daniel Hintz (2007; 2006) while it differs in interesting ways from the Quechua ‘II’ dialects of southern Peru as studied by Faller (2002; 2006). The analysis focuses on an orally performed traditional narrative that deals with the theme of social interaction between a human protagonist and a spirit being of the ‘other world’. It describes the human protagonist’s gradual realization of the nature of the spirit being with whom he has become involved; evidential and epistemic markings grammatically structure this transition from conjecture, to supposition, to direct witness. The aim is to show how the story’s cultural content, and the way in which evidentials and epistemic modality are operationalized, are mutually entailing. Form and content taken together throw light both on how evidentiality and epistemic modality work in social interaction and on how Amerindian understandings of the interface between the ‘natural’ and ‘supernatural’ worlds, and between ‘humans’ and ‘non-humans’, inform grammatical usage.