The main events of the book relate to the celebration around the issuing of a John Henry commemorative stamp, but it goes off on some tangents about the historical John Henry and more modern attempts to learn more about him (among other things). Going into the book, I had -- as probably many readers would -- only a vague idea of who John Henry was and what he did. The book not only counts on this, it plays it up. It opens with a series of recollections and hearsay about John Henry from supposed contemporaries or near contemporaries, all of which thoroughly contradict each other.
As to the composition that I enjoyed: Some books are like puzzles, with lots of little pieces that fit together to make the story whole at the end. This book was sort of like that, but not quite. It had some little pieces, but they were more like otherwise passing details from the main plot that were given an unexpected exposition. They didn't so much contribute to the events of the story as to give you a deeper sense of the characters' contexts (and the context the reader brings to the book as well).
