How does the novel explore the importance of the courage

Courage can be seen in the character of John Douglas. Douglas appears to be a faceless victim, simply the object of Holmes’ investigation. Towards the end of Part I, however, Douglas is revealed to be very much alive, and he commences to share his history, which comprises nearly the entirety of Part II. During this “story within a story," we learn that Douglas once bore the name “Jack McMurdo," and that he was part of a notorious gang in the United States, which was not unlike the Mafia. At the end of Part II, however, we learn that “McMurdo” is really a Pinkerton detective named “Birdy Edwards." Throughout all three of his “identities," Douglas is described as fearless, intelligent, and good-humored. Douglas is an example of Conan Doyle’s skill as a writer, in that the reader is able to accept with little difficulty the composition of the “three-in-one” character.