Answer:
because I choose to { dependent clause }
I do it { independent clause }
The thing that happen between chapter 21 and chapter 22 is the tone permanently changes to a more cynical attitude and this is the significant structural shift. The answer to this question is which asking about what happen between chapters 21 and 22 is that the tone permanently changes to a more cynical attitude.
The answer is "stacks." That is the object of the phrase, and since a person is searching for something ON the shelf, they aren't searching for the shelf itself.
