This article builds on recent research on Scandinavians in the international communist movement and on intelligence operations in Sweden before and during the Second World War. Through a microhistorical approach that centres around the Swedish communist cadre Ingvar Larsson, who was first an operative of the Comintern’s highly secret communications and courier network (OMS) and later was estranged from the communist movement, the article looks beyond structures and organizations, focusing instead on the choices and options of people driven by both ideology and opportunism. By exploring a diverse collection of Comintern, Soviet, and Swedish archival sources, the article highlights some of the peculiar challenges of intelligence history and of constructing a narrative in a way that illuminates both the agency of individuals and the wider culture of tensions and uncertainties between ideals and realities.