A sequence of firsthand journals, letters, medical notes, and newspaper clippings assembles a multipart account of travel to remote mountains, the arrival of a strange aristocrat, and a spreading pattern of inexplicable afflictions and nocturnal predations that endanger a small circle of acquaintances. The epistolary structure shifts perspective through personal diaries, clinical records, and a spoken phonograph entry, following the group's attempts to piece together folklore, empirical observation, and coordinated action to understand and counter the supernatural threat.