This chapter looks at the contribution of fantasy to theories about Tunguska. As American nuclear bombs dropped on Hiroshima and Nagasaki in August 1945, Soviet science fiction writers turned to the well-known Tunguska explosion with fresh eyes. Building on an established tradition in Russia of blending fantasy and science, engineer-turned-writer Alexander Kazantsev proposed that Tunguska had been caused by a nuclear-powered alien spacecraft that exploded over Siberia in 1908. In the years that followed, this fiction became a hypothesis and the source of significant and acrimonious public debate about the borders of legitimate science. As a subject of Cold War fiction, Tunguska reflected a new international orientation toward the relationship between fantasy and science. It also became fodder for further speculation and imagination about the relationship between Siberia and outer space — some of which played a productive role in scientific research as well.