In studies of professional learning, the rise of sociomaterial accounts draw attention to the political importance of nonhuman as well as human actors, the material as well as discursive, as inter-related in knowing and action. Of particular relevance to the issue of inter-professional work in health services, some researchers have argued that multiple worlds--not just multiple worldviews--are produced through socio-material processes. This article focuses on the complex activities involved in combining the multiple worlds of different professions with what some term para-professions. Such arrangements may not be recognised as inter-professional by their practitioners, with problematic consequences for care. The case is emergency mental health care, involving paramedics, police, hospital admissions staff, psychiatric nurses and A&E consultants. A sociomaterial analysis is used to trace how knowledge and practice circulates (or doesn't) within and across different material worlds of practitioners, and the ontological politics produced at their boundaries.