Daniel Burnham is a gifted architect who becomes part of the dynamic duo of Burnham and Root. John Root is considered the creative genius, and Burnham is the closer—he executes the designs and gets the business. When Root dies unexpectedly after they are hired for the fair, Burnham is tempted to quit, but he is compelled to prove his worth. He takes on the challenge of guiding his vision of beauty for the White City and successfully brings the fair to completion—a vindication both for himself and for the city of Chicago.
H.H. Holmes is a violent psychopath who possibly killed even before adulthood. Holmes has no moral center or respect for the law; he commits bigamy and various other types of fraud as well as multiple murders. Holmes gets a medical degree and then comes to Chicago to make his fortune. He is irresistible to many women; he seduces and then kills them when they no longer serve his purposes. Killing gives him an enormous sense of potency, both sexual and otherwise.
Frederick Olmsted is the country's foremost landscape architect. Nearing the end of his career, he reluctantly agrees to landscape the desolate wasteland of Jackson Park for the Chicago World's Fair. In the process he suffers many ailments and constantly fears that others will wreck his design. Although Olmsted must often use surrogates in Chicago, his landscaping efforts are a success, and he is mostly satisfied with the outcome.
Frank Geyer is a dogged, thorough, and smart detective who is assigned by the Philadelphia police department to find the three missing Pitezel children, who were traveling with Holmes a short time before Holmes was arrested for the murder of their father. Geyer travels to several states and Canada as he retraces Holmes's steps using the letters the children wrote that were never mailed. In the end, he finds the bodies in Toronto and Indianapolis.