"Heart of a Samurai" is a novel that is based on a true story by author Margi Preus. In this novel, Manjiro is a boy fishermen who gets lost at sea with the fellow fishermen from his village. When their boat washes up on a deserted island, Manjiro and the other fishermen do what they can to survive until one day they are rescued by an American-based whaling ship. Because it is the 19th century, Japan still has an isolationist attitude toward outsiders, so once the Japanese fishermen are rescued, they are not able to return to their country without the fear of facing imprisonment.

Manjiro and the other fishermen live on the American whaling boat for some time until they reach the Hawaiian island of Oahu. Here, the other fishermen find a home, while Manjiro decides to go on to live with the captain as his son in Massachusetts. When the captain and Manjiro reach Massachusetts, the captain remarries so that John Mung, Manjiro's American name, can have a normal boyhood.

Manjiro goes to school. Once he learns everything he can in elementary school, he enrolls in the local navigation academy. Manjiro continues to face adversity because of his race and origin, but he also has an opportunity to fulfill many of his hopes and dreams. In his late teens and early adulthood, Manjiro gets the opportunity to rescue his friends from Oahu and return to Japan, using money he earned when he finds some gold in the California gold rush. Upon their return, the fishermen are instantly imprisoned. When they are finally released, Manjiro returns to his village and family. He goes on to work with Japanese and American officials to foster a relationship between the west and Japan—finally fulfilling one of his long-term dreams.