What is the theme in Batman: The Long Halloween by Jeph Loeb?

The most recurrent theme in the book is that of the duality of man—the idea that people are split between their good and evil urges. The most obvious example of this theme is Harvey Dent. Throughout the book, Dent struggles with enforcing the law without breaking the law himself. When Dent helps Batman burn down a warehouse full of Carmine "The Roman" Falcone's money, Dent is tempted to steal some of the money for himself.