They called it Cru Sauvage. The impeccable Swiss packaging alluded to its aboriginal provenance, and inside were two bars wrapped in golden foil, 68 percent cacao. I'd paid $13 (plus shipping!) for these skinny little planks of chocolate, just 100 grams' worth of "Wild Vintage." That's $60 a pound. After savaging its wrapper, I placed a square of the dusky stuff on my tongue and closed my eyes.

Chocolate is the one of the most complex foods we know. It contains more than 600 flavor compounds. (Red wine has only 200.) Chocolate can be bitter, sweet, fruity, nutty, and savory all at once. It takes the vast library of taste and blends it into one revelatory package. The tropical cacao tree has secret things to tell us about flavor and desire, and for more than a decade I've made a hobby of tracking down those secrets.

This incredibly rare and expensive chocolate was produced by the venerable firm of Felchlin, which claimed that it was unique in the world, made from an ancient strain of cacao native to the Bolivian Amazon—i.e., wild cacao, au naturel, unmolested by millennia of botanical tinkering. It hit me with an intense nuttiness, but without the slightest hint of bitterness, a combination I'd never experienced. Aromatics burst in my sinuses. Citrus and vanilla. The flavor dove into a deep, rich place, and then, just as I thought I had a handle on it, the bottom fell out and it dove some more. That might sound ridiculous, but I've spent an inordinate amount of time "researching" the best chocolate in the world, geeking out on it like the most obnoxious sommelier, and this was something entirely new.

When the feeling finally began to subside, I opened my eyes and started looking for the man responsible.

HIS NAME WAS Volker Lehmann, and he was the only reason Cru Sauvage existed. Before I'd even tasted the chocolate, I'd gleaned the basic elements of the story from the folks at Felchlin: Agronomist enters Bolivian rainforest and makes startling discovery. Volker was the visionary connoisseur on the ground, in the shit. Felchlin was just smart enough to recognize what he'd found. The company invested in specialized equipment, began production, and brought the first fruits of Volker's labor to the European gourmet market, in small quantities, in 2005. It was three years before I heard of it.

After my own chocolate enlightenment, I had to know more. It wasn't easy making contact with Volker, but once I did, he told me he was just scratching the surface. Demand greatly exceeded supply, and there was much, much more out there. He was planning a trip to Bolivia's Río Grande, a remote tributary of the Amazon that, it was said, held vast chocolatales, as the forests of wild cacao are called. There he would visit the Amazonian tribespeople who lived along the banks, offer them employment as cacao gatherers, and eventually, he hoped, set up jungle processing stations in their villages. Did I want to tag along?

Yeah, I was in.

Six frustrating months later, on the other side of a series of false starts, logistical snafus, tropical deluges, and cruel vaccinations, I finally met the bald, athletic 53-year-old in the jungle city of Santa Cruz, Bolivia. From there, we hopped on a 16-seater to Trinidad, a swampy town with frogs trilling in the crumbling gutters. It was early March, the tail end of the rainy season; the rivers had risen 30 feet and spilled across the forests. Trees stood in six feet of water. Piranhas had abandoned the river channels for better hunting in the woods.