The story takes place in the United States in the 1970s. The relationship between Ruth (Rooney Mara) and her boyfriend Bob (Casey Affleck) is very good. Under the bright sunshine of Texas, when both of them thought that such a happy life would continue, misfortune came. In an accident, Ruth accidentally shot and killed a policeman and faced a severe trial. In order to protect the woman he loved, Bob was willing to go to jail to replace Ruth's crime. Not long after, Ruth gave birth to a lovely and beautiful baby girl. This news brought new hope to Bob who was imprisoned. As time went on, Bob's thoughts on Ruth and his daughter became stronger and stronger. Finally, a series of accidents made Ruth determined to escape from prison. However, at this time, Bob did not know that everything in the world outside the iron window had changed.