An incredible journey on the wings of butterflies.

My butterfly obsession began in a yoga class. My body was jackknifed in the downward dog pose. But my mind was far, far away, in the Central Mexican states of México and Michoacán. The area's boreal forests are the winter haven for more than a billion monarchs. The entire story line of a novel downloaded itself into my brain as if my muse simply pressed her "Send" button. My imagination invented a protagonist whose mission would be to save this endangered place, and because she's dying, she has less than a year to do it.

After that yoga class, I started to notice butterflies everywhere. Fluttering down city streets in the winter, intricately tattooed on women's bodies, even appearing in my own children's artwork. The butterflies were speaking to me. So I started writing.

Three years, four drafts, and hundreds of research hours later, I decided to retreat from fiction into reality and actually visit what would eventually appear in my novel—the Kingdom of the Monarchs, a 60-square-mile area in Central Mexico's volcanic highlands. Gamely, my imaginary heroine and I set off to a remote, ethereal place that monarch expert Dr. Lincoln Brower once called the Eighth Wonder of the World.

I am rolling through Mexico City, its sleekly modern skyscrapers giving way to neighborhoods of Spanish-style mansions with flowering purple jacaranda trees and then bucolic countryside fecund with peach and avocado orchards. I continue through a string of towering active volcanoes. I learn that the locals make a yearly pilgrimage to dance and offer flowers, clay artifacts, and turkey blood to keep the snowy-peaked Nevado de Toluca volcano quiet.

Several hours later I reach my first destination, the tiny former mining town of Angangueo in Michoacán. This traditional village has cobblestone streets and white stucco buildings with red-tiled roofs. No one speaks English.

After a quick hotel lunch at Plaza Don Gabino—fish roasted in cornhusks, homemade tortillas, and the creamiest guacamole on Earth—my butterfly safari begins.

I climb into an open-air truck, which begins a steep ascent up the mountain. I pass homes with outdoor birdcages, pots of red and pink geraniums, and freshly washed baby clothes drying on tree branches. Little kids kick a ball, and an old lady throws rocks (big ones!) at a pack of scuffling dogs.

Of the four monarch sanctuaries open to the public, I'll visit three. From the entrance of my first, El Rosario Monarch Butterfly Sanctuary, 129 miles west of Mexico City, I begin the hour-long hike up. The air is thin and getting thinner.

I pass other visitors on their way down.

"Worth it!" they say, jubilantly.

A Mexican grandmother stops to inform me in hand gestures that a butterfly landed on her hat.