Lee's selection of The Gray Ghost was significant for a variety of reasons.
First of all, the title alone is suggestive of Boo Radley. When Scout finally meets Boo, she notices how white he is. They have been calling him a ghost name for their whole understanding of his existence. They told stories about him as if he was a phantom or ghost.
Second, the character in the story named Stoner's boy had never really done anything wrong. People had just misjudged him. This is important because it was the very thing that people had done to Boo Radley.
Finally, this character actually turned out to be a hero just like Boo was for Scout and Jem. Although Scout doesn't draw the connections for the reader because she is falling asleep while talking with Atticus, she certainly reveals information that leaves readers the opportunity to draw conclusions in Chapter 31 after she had walked Boo home.
I love when a theme is wisely dropped by the author into my lap at the close of a novel. I feel reassurance knowing that what I have learned through my reading experience is right on target with the purpose of the novel.
In the concluding dialogue of To Kill a Mockingbird, Scout and her father Atticus discuss how a main character from The Gray Ghost, who was thought to be a strange and mysterious no-good-doer, was actually misinterpreted by the other characters. This character for The Gray Ghost, Stoner’s Boy, was found innocent in his story, and as Scout says, “…he was real nice.” To which Atticus replies, “Most people are, Scout, when you finally see them.” And, as the curtain falls on TKAM, we are gracefully handed a life lesson with a little help from The Gray Ghost, and Ms. Harper Lee’s brilliant mind.
The use of The Gray Ghost, by Ms. Harper Lee, is a parallel to Boo Radley’s character throughout TKAM. And, a reader has to wonder, was Dill a wise young man for offering up such a read as a reward when he challenged Jem to tread onto Boo’s property early on in the TKAM story? Or, was it just by chance that The Gray Ghost was the novel he was toting around with him that day. I have a hard time believing Ms. Lee would leave that significant of prop up to chance.