Early X-ray diffraction patterns from oriented fibres indicated that DNA must have a simple, repetitious structure and encouraged some researchers, who were already convinced that DNA was the genetic material, to undertake more detailed diffraction analyses and speculative modelling. The pioneering experimental work by Wilkins in the Wheatstone Laboratory at King's College London in the late 1940s first inspired, and then was overtaken by, the conjectural modelling of Watson and Crick in the Cavendish Laboratory at Cambridge. Why this was allowed to happen is still something of a puzzle. Here, I explore the puzzle and expose a peculiar flaw in the details of the original Watson-Crick model that was left for Wilkins to resolve.