Along the journey Gwynne approaches strangers (people in bars, garage attendants, chefs, waitresses, bus drivers, etc) and asks them to read extracts from the letters written over the last five years. In this way we not only get to learn about the friendship. We also get a feel for the strange towns and characters along the journey. We visit restaurants and order food exactly as written in Jim's letters.

Penumbra opens in Ireland with snippets of Ireland and some of its people. We then move on to Boise Idaho where we meet Jim's Mother and step father. It is at this point in the film that we learn that Jim is in prison. The journey continues down through Nevada and California where Jim's brother Hiram lives. Hiram brings us on a tour of houses and schools that Jim and Hiram lived in and attended as children. He also reveals his lack of contact with his brother. We also meet a good friend of Jim's.

Finally we arrive in Arizona where Jim lives. The letters have become less light-hearted and begin to describe conditions in the prison. Once we arrive at the prison it is revealed that Jim is on Death Row. Gwynne visits Jim and gives her reaction.