Textbooks usually remember the Triangle Fire as a turning point in the movement for improving worker safety conditions in the United States. It is a seminal event in the Progressive Era, which includes many such reform movements. The young women who perished in the Triangle Fire were victims, but the horror of the event led to reforms. In Triangle, von Drehle demonstrates that the injustices at the Triangle Shirtwaist Factory, and indeed in the garment industry more generally, did not begin or end with the fire. In the first two chapters, for instance, he begins to explain why the event at Triangle was "the crucial moment in a potent chain of events" that led to state and national reform. He does this by showing the potency of the forces arrayed against factory workers, as well as the beginnings of a political reform movement. In the first chapter, he discusses the background. The beating of Claire Lemisch by a career criminal named Charles Rose exemplifies the ways in which New York politics, local law enforcement, and the brutal competition between factories conspired against the predominately young, female, immigrant labor force. The role of Tammany Hall, headed by Richard Croker, in squelching worker radicalism and bourgeois reform, is highlighted.

The second chapter details the outbreak of the strike itself. In 1909, a major strike occurred, one rooted in the working conditions in the garment industry, which ranged from the abysmal (sweatshops) to the barely tolerable (factories like the Triangle itself). The largely immigrant workforce worked for long hours, under tight supervision, and in extraordinarily tedious jobs. Part of this was borne of increasing competition among the owners of the factories, who were themselves mostly immigrants. Isaac Harris and Max Blanck, the owners of the Triangle firm, were immigrants, but far from having sympathy for their workers, they instead ruled their factory with an iron fist. Their behavior, and that of people like them, led to the outbreak of a strike in which the Triangle workers emerged as prominent figures. Indeed, as von Drehle makes clear later in the book, one of the reasons the tragic fire had such resonance was that the Triangle factory and its workers were already well-known for their roles in the strike.

The opening chapters of the book are called "The Spirit of the Age" and "Triangle." In short, both chapters are meant to present the corruption at the Triangle Shirtwaist Factory before the fire begins.

The first chapter is called "Spirit of the Age" because of the horrible corruption it highlights. The very first words are that "burglary was the usual occupation of ... Charles Rose" who was hired to beat up a female strike leader named Clara Lemlich.

[Clara represents] the drive for women’s rights (and other civil rights), the rise of unions, and the use of activist government to address social problems.

The chapter focuses on the character of Clara, her family, and her job in the clothing industry as a low-wage earner turned protester. The brutal physical attack on Clara ordered by Charles sets the scene. The environment that follows is one the pits the employers against the workers.

In the second chapter, the character of Kline says he is "sick of the slave driving" at the Triangle. Kline wants more money and improved conditions. Any worker who sides with Kine is ordered to leave, but no one moves. During the course of chapter 2, the original standoff by Kline threatens to turn into a full-blown strike. "Progressive women" (like Clara from the first chapter) are being hauled off to jail by Tammany cops, and political corruption is allowing this to happen. Issac Harris and Marcus Blanck, the owners (the "Shirtwaist Kings"), begin the press releases to halt the coming strike from the "shirtwaist union." By the end of chapter 2, a confrontation "becomes inevitable." Blanck and Harris demand to form an "EMPLOYERS MUTUAL PROTECTION ORGANIZATION" (purposely written in all capital letters) in order to counteract the forming union.

These chapters are important because the eventual flames at the Triangle Shirtwaist Factory fire would trap and then kill some of the strikers working the hardest to change labor laws and horrible conditions for workers. Why would the fire kill so many? All but one of the fire exits are locked to prevent both theft and unauthorized breaks by workers.