For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
All Tied Up
Prometheus gets chained to a barren rock in Scythia for the very, very minor crime of stealing fire from the gods and giving it to humans.
Act II
Look Into My Crystal Ball
Various characters show up and try to convince Prometheus to submit to the authority of Zeus. Prometheus refuses, because he knows that Zeus will father a child more powerful than he is, who will kick him off his throne. And that child? Descendant of Io. So Prometheus isn't feeling much like submitting, thankyouverymuch.
Act III:
EXTERMINATE
Hermes comes and tries to convince Prometheus to reveal more details about Zeus's destiny. Prometheus refuses. A huge storm (presumably sent by Zeus) starts brewing. The earth opens up and Prometheus falls into a chasm.