While vacationing in Puerto Vallarta in fall 2008, USC professor Deborah Harkness, a historian of science, was consumed with the upcoming bicentenary of Charles Darwin's birth, but the rest of the world, including the airport in the Mexican resort city, was gripped by a madness spread by vampires: The last of Stephenie Meyer's four "Twilight" novels had just been published.

"To walk through the airport was to be hit with vampires, witches, ghosts and demons at every angle in the bookstores," says Harkness, a good-humored and enthusiastic woman of 46, over a cappuccino in Pasadena.

"It was so huge — it seemed to me much bigger than what had happened with Anne Rice. And as a historian of science, trapped in Puerto Vallarta during what turned out to be the rainy season, I thought, 'Why do these creatures still exert such a pull on us?' "
The whole thing felt to her like a throwback — a throwback of 450 years. "People believed that the supernatural and the natural existed, intermingled. We think of ourselves as having very little in common with people in 1558. And yet there were walls of this stuff. What if 16th century people were right, and the supernatural and natural coexisted? How would that play out? It started out almost like a kind of logic problem."