It was a sweaty night of tropical heat when our van pulled up to the curb on a narrow backstreet outside Monterrey, and our team of a dozen conspicuous Americans climbed warily out of the air conditioning.

Small pockets of neighbors stared from the shadows as Latin music thumped in the background. We got our first look at the Mission where we'd be staying for a week, and the barred windows were not an encouraging first impression. We hastily entered the protection of the stucco-and-concrete courtyard, exhausted from our trip—and overwhelmed by the strangeness of it all.

Later that night, after lugging duffels inside the protective gates and brushing our teeth at a cold-water tap, we climbed a rough outside stairwell to our sleeping quarters. That's when Tara, one of our team members, happened to come up the steps behind me.

Tara had spent a semester during college in Central America, so she was much more comfortable with her surroundings than the rest of us. "Do you want to see a Mexican ...