The two young men, euphoric about cracking this problem so quickly, invited Wilkins and his assistant, Rosalind Franklin (a very talented x-ray crystallographer whose work with DNA was critical to its eventual solution) in from King's College to the Cavendish to see their triumph. Franklin tore it apart. The problem was not only the assumption that their molecule was helical-Franklin was not convinced that the x-ray data proved that it was-but their idea that positive ions cemented the center together. Magnesium or any other ions, she pointed out, would undoubtedly be surrounded by water molecules in a cell nucleus and rendered neutral. They could not hold the phosphates together. And water was important. Crick and Watson, she pointed out, had gotten some data wrong. According to Franklin, DNA was a thirsty molecule, drinking up ten times more water than their model allowed. The molecule's ability to soak up water indicated to Franklin that the phosphates were on the outside of the molecule, where they could be encased in a shell of water. The wrong water content also meant that Crick and Watson's density calculations were off. Their model, it became clear, was deeply flawed.

Franklin was opinionated, outspoken, and correct. The two young men tried to convince Wilkins and Franklin to collaborate with them on another attempt but were turned down. When news of the fiasco reached Bragg, he quickly sent Crick back to proteins and Watson to something more in keeping with his background, a crystallographic study of tobacco mosaic virus. But the pair, Watson in particular, did not stop thinking about nucleic acids. Pauling remembered Watson as "something of a monomaniac" where DNA was concerned, and rather than give up on the problem, he and Crick took it underground, talking it over quietly in their office or over drinks at a local pub. They might have gotten one model wrong, but they were certain their approach was right. Perhaps all they needed was a little more chemistry. For Christmas 1951, Crick gave Watson a copy of Linus Pauling's influential book, The Nature of the Chemical Bond. "Somewhere in Pauling's masterpiece," Watson remembered, "I hoped the real secret would lie."