Sylvia M. Payne was one of the first women to practice psychoanalysis in Britain. Though she became president of the British Psychoanalytical Society, not a single scholarly work is dedicated to Payne's intellectual ideas - a substantial historical lacuna, especially when compared with the research on Ernest Jones, one of Sigmund Freud's early disciples and the president who preceded her. This essay presents the first exploration of her early work. It focuses on her belonging to a group of British analysts who challenged Sigmund Freud's thinking on sexual difference. The full scope of this challenge, I argue, as it emerged in interwar Britain, has remained unexamined until today. Adding to the scholarship on the prominent and lesser-known roles of women in psychoanalysis, the article shows that Payne made significant contributions to the field; she also developed the work of Melanie Klein, on whom we also need more research. The study describes the life and work of a woman who has been neglected in the historiography of twentieth-century intellectual history. It engages with broader methodological questions of how to define the political, historical role of female psychoanalysts of her generation.