Chapters 1–10

In the opening chapters of The Double Helix, the key figures involved in uncovering the structure of DNA are introduced. Watson skillfully intertwines character sketches with the narrative of his arrival at the Cavendish Laboratory in Cambridge, England. Here, he begins to form connections with fellow scientists, some of whom become allies while others are rivals. As a young man from the Midwest embarking on his first major adventure, Watson concludes that "a scientist’s life might be socially engaging as well as intellectually stimulating," a philosophy he embraces through activities like hiking in the Alps and "midnight excursions to waterfront bars."

Watson's primary objective at the Cavendish Laboratory is to explore the molecular structure of proteins by constructing three-dimensional models. Upon meeting Crick, whom he describes as never having been seen "in a modest mood," Watson is thrilled to find a colleague who shares his fascination with DNA research. Since the DNA molecule is too small to be viewed through a microscope, it can only be "visualized" in its crystallized form using X-ray techniques. However, neither Watson nor Crick possesses advanced skills in crystallography, necessitating the assistance of experts at the competing King’s College in London to obtain images of the molecule. This brings Maurice Wilkins and Rosalind Franklin into the story. Although these two "colleagues" act more like adversaries, both are engaged in DNA research through crystallography at the King’s College laboratory.

The three male scientists form a friendship, while Franklin is depicted as a woman with "combative moods" who does "not highlight her feminine attributes." Despite this, Wilkins recognizes that he requires Franklin's expertise to compete with Linus Pauling, who is also investigating the DNA enigma at his California lab. Watson and Crick grasp the predicament as well and resolve to extract as much information from Franklin—by any means necessary—to outpace Pauling in solving the mystery. The closing line of Chapter 2, "The thought could not be avoided that the best home for a feminist was in another person’s lab," encapsulates the tense atmosphere at the King’s College laboratory.

In Chapter 10, Watson attends a presentation by Franklin, who describes the DNA molecule as having a helical shape with a sugar-phosphate backbone on the exterior. However, Watson fails to take notes during the lecture, relying instead on his memory to recall Franklin’s theory. This oversight will prove to be a significant setback in his and Crick’s efforts to construct a DNA model.

Chapters 11–21

In the middle section of the book, the narrative focuses on an experiment that sets Watson and Crick back by approximately a year in their DNA research. Watson, unable to recall Franklin's exact words from her lecture, provides Crick with incorrect information regarding her proposal. The primary error in their resulting model is placing the backbone on the inside, contrary to Franklin's assertion. Despite their confidence in this "discovery," Watson and Crick present their model to Wilkins and Franklin. It doesn’t take long for Franklin and others to dismantle their idea, proving it to be both incorrect and absurd. Upon learning of this failure, Lawrence Bragg, the Nobel Prize-winning director of the Cavendish Laboratory, instructs Watson and Crick to cease their DNA research and leave it to the scientists at King’s College.

Over the following year, Crick focuses on completing his doctorate, while Watson turns his attention to studying the tobacco mosaic virus (TMV). Watson notes, “A vital component of TMV was nucleic acid, and so it was the perfect front to mask my continued interest in DNA.” During this period, Watson also invites his sister to visit England for extended...