A scientific inventor builds a device that permits travel through time and recounts journeys to distant futures. He observes a fragile, surface-dwelling humanity living in passive leisure and a subterranean, industrial species that sustains that condition through hidden labor, exposing a stark social and evolutionary division. Subsequent visions trace the slow decay of the planet and the diminishing of life under changing cosmic conditions, punctuated by strange relics of former ages. He returns to relate these discoveries and their implications for social order and human transience, then departs again into time, leaving his ultimate fate uncertain.