I think that one interesting point to draw from the novel as a whole is the contrast between the "white" city of the World Fair, and the dark nature of the serial killer, Holmes. Larsen blends fact with fiction to create this story, but in totality it creates the argument that beauty can be a facade that just barely covers the dirty, awful behavior hidden the surface. The World's Fair was intended to bring the best and brightest things to Chicago, and for Chicago and the United States to show off its glory, but the actual construction was done cheaply with the intention for the buildings to only be pretty for the 6 months of the fair and to be only temporary structures. Just as the Fair is a show, so is Holmes' character. He appears one way on the outside, and yet is pure evil. He uses the cover of the Fair to hide his crimes. Just as the designers of the Fair want to produce something great, they also had their petty, ugly disagreements behind the scenes. I think you could craft an interesting analysis of the theme of appearance versus reality.