What happens in The City of Ember, The Prophet of Yonwood?

In "The City of Ember, The Prophet of Yonwood," what exactly takes place within the city of Ember? Are there any significant events or turning points that occur? How does the Prophet of Yonwood factor into the story and what role does he play? Are there any conflicts or challenges that the characters face as they navigate through the city and its mysteries? Additionally, how does the setting of Ember contribute to the overall narrative and themes of the story?