You are in luck! eNotes has several pages dedicated to Prometheus Unbound, including a summary. I am happy to give you a short summary here, but please consult our pre-existing webpages for more details.

Prometheus Unbound is the name of a lyrical drama, written by Percy Bysshe Shelley and published in 1820. The play concerns the ancient Greek mythological beings called Titans and focuses on Prometheus, who has been punished by Jupiter for giving fire to the humans. Much of the play deals with Prometheus' struggle to overcome Jupiter and act on behalf of the humans who are now slaves to heaven, with no free will. Prometheus is aided by his love, Asia, who reveals to him the ideals of Truth and Beauty. The final act of the play occurs after Jupiter has been overcome and describes the beautiful new world where humans are restored to freedom.