Earth on Fire is the story of a young woman, Hetty Marshall, who decides to make a documentary about her brother John. John has been studying to enter the priesthood and is scheduled to give his first sermon on the day she arrives.

Upon arriving, Hetty finds that John has disappeared. When he returns, he no longer feels he has the devotion necessary to be a priest of a church he can no longer believe in.

John takes to the street, gathering a number of followers: Peter, a well-off young man who has become distanced from his family. Simon, an angry local activist. Sarah, a homeless young mother.

As he travels, he begins to address not only issues concering the church, but issues concerning the whole of the country. John comes to believe that the generational conflict in this country is tearing American apart.

This message is not received well in all corners, and John begins to make enemies within the community.

As John's movement grows, Michael, a local radio personality, opens up his show as a forum for both John and the town establishment to talk freely. The conflict that arises from that meeting threatens to consume both John and those who have heard what he has had to say.