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
The prologue: you learn that the factory at R.U.R. has created robots, which will end poverty and usher in gladness. You're introduced to the main characters Domin and Helena, who marry at the end of the act, even though Helena doesn't really want to.
Act II
Acts 1 and 2 (ten years after the prologue): the robots revolt and kill everyone, except the head of construction at the factory, Alquist. The formula for creating robots is lost as well, so basically everyone will die and life on earth will cease. That's a real downer, Act 2.
Act III
Two robots turn out to have souls and they fall in love. Alquist believes they'll reproduce because he's rediscovered the formula for life. Does that formula involve making robots or making babies? It's unclear, but be happy anyway.