The British researchers wanted to talk to Pauling. There were too many loose ends, too much conflicting data from the growing number of researchers in the protein field to allow clear conclusions about the importance of Pauling's work. So they invited him to England to explain himself, listen to alternative interpretations, and take questions. A special London meeting held under the auspices of the Royal Society was to be devoted to protein structures, with Pauling featured as first speaker, followed by Corey, then a series of presentations from leading British protein scientists. It would be a chance to examine and debate the validity of Pauling's structures. The date was set for May 1, 1952.

Pauling was eager to go. Through the end of 1951 and into the early months of 1952 he and Corey rechecked, reconsidered, and refined their structures. Special attention was paid to the disputed structures for muscle (which Pauling, after preparing hundreds of samples of dried muscle, now concluded was mostly composed of alpha helixes, with about 10 percent of some unknown structure) and collagen (Pauling and Corey decided after an exhaustive review that their three-cable structure was probably right, despite British doubts). Corey, meanwhile, mounted a full-scale assault on lysozyme, a globular protein, hoping to become the first person to describe the structure one of these tightly-packed, soluble molecules, so different from the fibrous proteins he and Pauling had been analyzing. Lysozyme, however, proved too challenging; by the spring of 1952 Corey had little to show for his efforts.

Pauling began making plans not only to attend the Royal Society meeting, but also to visit major British crystallography centers, tour Spanish universities, and take a swing through France during which he would pick up an honorary degree from the University at Toulouse.

Then all his plans came undone. On Valentine's Day 1952, Mrs. Ruth B. Shipley, head of the US State Department's passport division, responded to Pauling's routine request for a passport with a flat denial. Shipley, a died-in-the-wool anti-Communist, was delaying or denying visas and passports to anyone she considered detrimental to the interests of the United States. Pauling, she thought, at best was a bad spokesperson for America, and at worst was a likely Communist. Allowing him to spread across Europe his anti-American ideas and criticism of nuclear policies was unacceptable.

Pauling tried for weeks to get the decision reversed, writing everyone from the head of the National Academy of Sciences to the President of the United States. In the end, however, after a face-to-face meeting with Shipley and at the last possible minute, he was denied his right to travel, forced to cancel his flight, and compelled to wire his regrets to the Royal Society.

The British protein researchers were incredulous. Many of them learned the news the day before the start of the meeting, at a formal tea that Pauling had been slated to attend. One of them later recalled "the shock that it produced, the outrage at the stupidity of the State Department at detaining the great man as if he were a dangerous character."