The play concerns the god Prometheus, who in defiance of Zeus has saved humanity with his gift of fire. For this act Zeus has ordered that he be chained to a remote crag. Despite his seeming isolation, Prometheus is visited by the ancient god Oceanus, by a chorus of Oceanus’s daughters, by the “cow-headed” Io (another victim of Zeus), and finally by the god Hermes; who vainly demands from Prometheus his knowledge of a secret that could threaten Zeus’s power.