Drawing on data generated in collaborative biographical story-telling groups with migrant women in rounds of stories, this article deals with the dynamics of power and knowledge displayed by migrant speakers in a situation of diaspora. I focus on a sexual harassment episode shared by one female Brazilian migrant speaker, Flavia, in relating a crucial moment of change in her life history. The study was structured to gain a perspective on this biographical rupture from three angles, namely successive rounds of stories, the story-telling interaction, as well as the circulation of knowledge displayed by speakers and textual objects they produced across situated interactions. The various perspectives bring to light a language biographical juncture, or muda, i.e. a meaningful, internalized, enduring and embodied re-socialisation into a new linguistic environment. An analysis of the moment by moment subjectivation process revealed this participant subalternally positioned as a woman, a Brazilian migrant and a speaker, hence, as a new citizen in Portugal framed by a set of different varieties of Portuguese permeated by (gendered) coloniality. I illustrate how a combined focus on the socio-material dispositions, on the production of discursive selves and on intersubjectivity in the rounds of stories helped to disclose the material and discursive workings of power and knowledge. Participants biographized themselves as migrants and speakers, with embodied, emotional and enduring biopolitical implications. Finally, the article discusses the extent to which the dispositions and affordances of biographical research, as acts of biographization, contribute to capturing the biopolitical nature of a language muda.