FOR FOUR DAYS NOW, my buddy Tim and I have been ripping around central Mexico tasting tequilas. We've visited distilleries and factory stores in the 7,000-foot highlands east of Guadalajara. Here to the west, on La Ruta del Tequila, we've followed the government-designated "Tequila Trail," which circles a low volcano while passing through municipalities where the liquor is made, including El Arenal, Amatitán, Tequila, and Magda­lena. On La Ruta, most of the other tourists are Mexican couples looking for old set locations of a popular telenovela called Destilando Amor ("Distilling Love"). We're here to drink the world's finest tequilas.

Today is a lazy day-we're tired and a little hungover-so when Tim and I swing into a cantina between Amatitán and Tequila in the afternoon, it's just to see what's up. The open-air highwayside bar is called Jarritos el Guero and serves a Mexican margarita made with fresh grapefruit, orange, lime, salt, and a splash of Squirt. As we make our way across the patio, a voice from behind calls out, "Hi!"

Five women in their early twenties, all wearing the canary-yellow polo shirts issued to employees at the Cuervo factory and museum down the road, beckon us over. The women explain in English that they recognized tall-hair, big-smile Tim from our tour yesterday.

"Why do you drive all the way out here to drink?" I ask. "Don't you get free liquor from Cuervo?"

"Yes," one of the women says, "but this tequila is the best!"

She offers her clay mug, and, sure enough, the tequila inside seems uncommonly smooth and strong. But it's tough to say much more than that, since the flavor is buried by citrus. "What is it?" I ask.

She says it's a high-proof bootleg called De la Sierra. Who makes it, and where, is a mystery. The women provide various contradictory answers-"It's made by drug runners"; "It's made in the hills over there"; "No! Over there"-but they take off before we can sort things out.

We haven't really tasted this secret tequila. We don't know where it's distilled. But we've got to find it. Fate or felicity has brought us here. The Cuervo ladies have pointed to the horizon.