Kate O'Brien's work is now widely considered canonical in the English language, and the author herself an icon for Ireland seeking to reinvent itself. O'Brien's novel, Mary Lavalle, banned upon publication in 1936, is a key work of the twentieth century that has suffered from critical neglect despite its wider popularity with readers. This book reexamines Mary Lavalle, exploring its role in the modernist canon and its importance to political and queer activism. The novel's biographical and autobiographical experimentation is of particular note. Additionally, through the lens of this crucial novel, the oeuvre of Kate O'Brien is recontextualized and reassessed.