[1] The dramatis personae are Prometheus, Cratus (Power), Bia (Violence), Hephaestus, the mortal woman Io, Oceanus, Hermes and a chorus of Oceanids.
The Olympian transformed her into a cow, and a gadfly sent by Hera has chased her all the way from Argos; Prometheus forecasts her future travels, telling her that Zeus will eventually end her torment in Egypt, where she will bear a son named Epaphus.
A fragment translated into Latin by the Roman statesman Cicero demonstrates that the chorus of this play is constituted by a group of Titans, recently freed from Tartarus by Zeus despite their defeat in the Titanomachy.
Again mirroring events in the previous play, Prometheus would forecast Heracles' remaining travels as he completes his Twelve Labours.
[3] Despite the paucity of direct evidence, Prometheus' foreshadowing of future events in the trilogy's first play suggests that the final play concerned itself with Prometheus' knowledge of a secret that could potentially lead to Zeus' downfall, and how the revelation of this secret leads to reconciliation between the Titan and Olympian.
The secret is this: the sea nymph Thetis, whom Zeus wants to take as a lover, is fated to bear a child greater than its father.
Some scholars have taken this to mean that in the Unbound, Prometheus prophesies that eventually (in the Fire-Bringer), Zeus would reconcile with him, and establish some sort of festival in his honor.
Given the title of the play, and taking a cue from the aetiology for the Athenian Areopagus provided by Aeschylus' Eumenides, it has been suggested that the drama concludes with Zeus' foundation of the yearly torch race that took place in Athens to honor Prometheus.