Larson, writing about the 1890s Chicago World's Fair, uses Daniel Burnham and Henry Holmes to symbolize the two directions in which technology would go in the twentieth century.

Daniel Burnham, the architect who, with several others, masterminded the magnificent Chicago World's Fair, which showcased how far the world had come technologically in a hundred years, foreshadows the glorious achievements of twentieth century technology, such as moon shots and polio vaccines. He represents all the creative potential for good in modern invention.

Henry Holmes, coexisting side by side with Burnham in the same city, represents man's capacity to use modern technology and invention for evil. A sociopath and serial killer, Burnham, with his ingenious gas chambers and ovens meant to hide the evidence of his misdeeds, chillingly foreshadows the evil technology would be used for in the twentieth century.

By juxtaposing the stories of two men who represent extremes in the use and misuse of invention, Larson highlights that technology is a complicated force that can't be simply applauded or condemned, but must be handled with care.

Daniel Burnham and Henry Holmes were both brilliant in some ways, but Burnham used his brilliance to create, while Holmes used it to destroy. Burnham was the architect who created the magnificent World's Columbian Exposition of 1893--a formidable feat, given the hurdles he faced to get it built. The results were so opulent that "some [visitors] wept at its beauty" (page 6). The fair also introduced visitors to new experiences, including the sights of Egypt and the taste of Cracker Jacks. One exhibition hall had more volume than the U.S. Capitol, St. Paul's Cathedral, and several other large structures combined.

Dr. Henry Holmes (an alias), on the other hand, used the fair to showcase his capacity for malevolence. He constructed a hotel not far from the magnificent fair grounds that housed airtight vaults that were used as gas chambers. He also built a crematorium in the basement of his hotel. Holmes killed many young women who attended or worked at the fair, and he eventually admitted to killing 27 people (including three children). However, he may have actually killed more, as he dedicated his brilliance to causing death.

Larson alternates the chapters about Burnham with chapters about Holmes to contrast how Burnham worked to invent things that would bring joy to people, while Holmes used his considerable force and intelligence to create new ways to kill. The contrast between Burnham and Holmes is that Burnham used the new technology of his age to create, while Holmes, a devil-like character, used it to destroy.