What's for dinner? Where are we going? The element of surprise shapes Yo Soy Underground Suppers' unconventional (and delightful) meals.

Mikey Corona, bow tie-clad emcee for the evening, gives us a sly smile as he explains the dessert being set before us. "We're having cornmeal pound cake with saffron whip, sweet tomato chutney and just a sprinkling of sal de gusano. Does anyone know what sal de gusano is?" he asks, looking down the dining table for reactions. "A few people? OK, if you're not familiar with it, maybe don't look it up until after you've tried this."

I hesitate, but only for a second, and then dig into the tender cake. It's a symphony of flavors: sweet, tangy, creamy and just a hint of smokiness-the touch, I assume, of the mysterious sal de gusano.

You need a certain comfort with the unknown to dine with owner-host Mikey and owner-chef Brian Riggenbach, the duo who run Yo Soy Underground Suppers, an ongoing series of Mexican-theme pop-up dinners. The model matches that of "secret suppers" held in cities across the region: Guests reserve a dinner spot without answers to questions like "Where am I going?" and "What's on the menu?" until the day of the event. For Yo Soy, that means a noon e-mail with an address and a menu overview. But even that cryptic missive sheds little light on the experience.

After all, having an address doesn't convey the giddy in-crowd thrill of sharing a knowing nod with a stranger headed up the same walkway or the surprising reassurance of being welcomed like an old friend to an impressive and unfamiliar home. (In this case, it's a historical brownstone with an HGTV resume.) And seeing the words Indian-Mexican fusion (the theme for this particular dinner) doesn't convey the delight of discovering panipuri (an Indian street food) stuffed with Mexican ingredients like mole and queso fresco or of digging into enchiladas slathered in tikka masala curry.

And there's no way for the website's emphasis on a shared table ("one of the most important components to a great meal is the company") to convey the sense of serendipitous conviviality infusing a Yo Soy dinner. It's the kind of romance that occurs when a group of strangers, brought together by luck, share an exceptional meal, sitting shoulder to shoulder in a dining room that exists for just one night. It's a fleeting experience, and all the more exquisite for that.

The man sitting next to me has yet to touch his dessert; he's searching for sal de gusano on his phone. When he finds it, he leans over and asks conspiratorially, "Do you want to know what you just ate?"

I decline. Up and down the table, people murmur their pleasure. So far, all of my other questions about this meal have been answered; I'm happy to let a little mystery remain.

To attend: Reserve a spot at yosoychicago.com. Tickets run between $60 and $75 for your meal (gratuities not included), and it's BYO if you want a drink after the cocktail hour.