Joan shows up at the Castle of Vaucouleurs full of determination. She wastes no time in making her goals clear to Robert de Baudricourt and his soldiers. God has given her a mandate to unite France under Charles and give the English the boot. At the end of this stage she's off to the Dauphin, Charles, to make her dreams a reality.
Everything is looking good for Joan. She impresses the Archbishop, inspires Charles, and convinces the less jaded members of the court that she has been sent by God. Charles grants her command of the army, and she heads to Orleans. There she gains Dunois' respect with her courage. When the wind changes in a favorable direction for his ships, he's convinced that God is on her side. As the stage comes to a close, Joan and Dunois charge off to glorious battle.
Good things never last, at least in tragedies. In scene four, Warwick, the Chaplain, and Cauchon plot to try Joan for heresy. Her friends all give her the cold shoulder in scene five. Charles has been crowned and they're all ready to stop the fighting, even though France is not yet united. Joan, true to her mission, can't rest until the job gets finished. Charles, the Archbishop, and even Dunois all tell her that they'll do nothing to help her if she gets captured. Ultimately, Joan sticks to her guns and goes it alone.
True to the tragic structure, it is Joan who causes her own destruction in the end. She's given a chance to repent over and over again. For a brief moment, it seems like she will. She signs a confession saying that her voices were demons and that she was a bad, bad girl. When she learns that the Church is going to lock her up for life, she rips up the confession and chooses to be executed. Joan dies a firm believer in herself and God. In the epilogue, Shaw highlights the even greater tragedy of Joan. He uses a dream sequence to hypothesize that she wouldn't be accepted even if she came back to life as a saint.