The scene - which played out 50 years ago this week - is one of the most famous of 20th- century science. It marked the conclusion to an intellectual footrace to find the structure of deoxyribonucleic acid, better known as DNA.
Their discovery solved the fundamental mystery of heredity, how everything from eye color to crippling disease can be passed through generations.
A half-century later, historians are still filling in the details of the story behind the discovery and resurrecting old questions about who should get credit. In a tale that turns out to be as twisted as the strands of the double helix itself, the role played by a little-known chemist, Rosalind Franklin, is getting new attention.
In a biography published in October, author Brenda Maddox shows how Franklin's photographs and measurements of the molecule, which Watson and Crick acquired secretly, led them to a Nobel Prize. The book raises anew questions about whether the pair went too far and if Franklin's contributions were adequately recognized.
"Rosalind seemed doomed to remain the invisible woman in many minds, the faceless nurse who hands the surgeon the scalpel," Maddox wrote.
"They apparently fell into a kind of intellectual crush on each other," wrote science historian Horace Freeland Judson in The Eighth Day of Creation: Makers of the Revolution in Biology.
Born in Northampton, England, Crick was known for his nonstop talking and stiletto-sharp intellect. He had little to show for it - only the mines he designed for the British Admiralty during World War II. But his Cambridge colleagues soon learned that he had an annoying way of swooping in and attempting to solve their scientific problems.
Watson, meanwhile, was an eccentric skirt-chaser from Chicago who loped across the manicured Cambridge lawns in untied tennis shoes and shorts - even in the winter. He mumbled and had a bad habit of staring. But he was no intellectual slouch, graduating from the University of Chicago with a degree in zoology at 19.
Both altered their careers after stumbling upon physicist Erwin Schrodinger's book What is Life?, which argued that genes were the essential stuff of life. Nobody really knew what genes were made of, though DNA was one possibility.
The book inspired Crick, at the relatively late age of 33, to abandon physics for biology and pursue a doctorate at Cambridge. Watson, too, had become obsessed with DNA after reading Schrodinger and went to Cambridge with hopes of unlocking the molecule's secrets.
Although the two were officially assigned to other things, unofficially they spent most of their time talking about DNA over tea in Room 103 of the Cavendish Laboratory or over lunch at The Eagle.
"I daydreamed about discovering the secret of the gene," Watson later wrote.
Among the handful of scientists interested in DNA was Linus Pauling at the California Institute of Technology, a chemist who went on to win two Nobel Prizes. He had an unorthodox approach to solving problems: he liked to build Tinkertoy-like models of molecules, rearranging the pieces until they fit.