The tone of the story is reminiscent.
Tone is the author’s attitude toward a subject. The tone changes from scene to scene. Notice that the Tom Robinson story is framed by the Boo Radley story. The book focuses on an older Jean Finch looking back on her childhood, remembering the events that shaped her.
Notice how the book beings:
When enough years had gone by to enable us to look back on them, we sometimes discussed the events leading to his accident. I maintain that the Ewells started it all, but Jem, who was four years my senior, said it started long before that. He said it began the summer Dill came to us, when Dill first gave us the idea of making Boo Radley come out. (chapter 1)
It’s as if she is looking back at what happened, and re-examining events from a more mature perspective.
The tone is a bit nostalgic, as the book is being narrated by a much older Scout as she tells the story of a significant event that shaped her childhood. Since we are seeing Maycomb from a child's point of view, we have a limited scope.