Some of the very first theatre productions following the Russian Revolution of 1917 were built around Christian imagery and dramatic forms, a surprising choice given that atheism was a key tenet of the new Soviet nation. The first Soviet play, Vladimir Mayakovsky’s Mystery Bouffe, is modelled after the medieval mystery play and depicts workers coming to revolutionary consciousness after encountering a Christ-like figure. Subsequently, several of the earliest Soviet mass spectacles, a vibrant form of state-sponsored propaganda, also drew comparisons to mystery plays. This article examines the interdependence of theatricality and spirituality in these early Soviet mysteries (approx. 1918–21), referencing the context of church practice, the mystery play genre, and Russian symbolism’s earlier fascination with the mystery play. I argue that these Soviet variants on this medieval dramatic form struggle self-consciously with the ironies and the possibilities of borrowing from the mystery in the newly Soviet theatre. Their triumphant messages about socialism and the revolution are nuanced by the essentially religious nature of the genre even as they attempt to replace mystery with theatrical spectacle to create a new model of theatre. By revealing spiritual dimensions of socialist avant-garde aesthetics, these Soviet mysteries can enrich our understanding of both the place of religion in modernism and the consistency of modernist values.