We enter into The Devil in the White City a bit like we begin the movie Titanic: we already know what's going to happen in the end. Chicago will pull off the greatest world's fair in history and Holmes will pay for his murders, as surely as the ship will sink.
What the story then becomes isn't so much about how it's going to end, but rather how we get there. How does Chicago score the bid to host the fair? How do architects overcome obstacles? How does Holmes do what he does for so long and get away with it?
This book is about the journey, not the destination.
After going along for the ride, we're left with a few nuggets of knowledge in the end. Chicago's pride and determination gets the city the bid. Talented architects under the guise of Burnham transform desolate, icy soil into a magical White City. Exhibits like an entire Algerian village and neat inventions like automatic dishwashers fill visitors with a sense of wonder and awe.
Bonus: the world gets introduced to Cracker Jacks.
As for Holmes—the guy has a winning ticket. The fair means more travelers to Chicago, which means more women for him to lure into his murder castle. Sure, he can dodge the police when they come asking about victims, but even he knows he can't hold them off forever. In the end, it's his becoming close with one victim, Pitezel, and his family that ultimately leads to his demise.
It's not that Holmes makes any mistakes. Rather, he goes too far, getting lost in his thirst for more and more.
Burnham gets the last word…but it's not an uplifting one. By the end of the book, Millet has drowned, and Burnham loses one of his last connections to the great Chicago World's Fair of 1893.
Yeah. It's a bit of a downer.