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It's a cold and drizzly night in Mexico City, but love and commerce are in the air. As my half brother Uriel and I park outside Plaza Garibaldi, our vehicle is instantly surrounded by troubadours clad in tuxedos and sombreros, and clamoring for our business.

In the open-air square, there are dozens of mariachi crews tuning their instruments. Their guitar cases form little mountains everywhere. Embracing couples sway as some of the mariachis break into song.

The musicians here specialize in a uniquely Mexican niche: the emergency serenade. In Mexico, it is impossible to get serious with a woman - or to properly atone to her for a grievous error that you made - without expressing it in song from the sidewalk as she watches from her bedroom window. If you attempt to express love or contrition in another way (say, with a card) you are essentially a drifter with a single cross earring and a teardrop facial tattoo.

But you can't just show up outside your lover's house and start bellowing ballads. That's crazy-person territory. You need an entire band to back you up. For starters: a trumpeter, a guitarist, a cellist and a lead singer with a powerful-enough voice to drown out your own Joan Rivers-esque pipes. Preferably, these musicians should be wearing spurs and a lot of black suede.

And you need this band at 3 a.m., with no advance notice. Because who hires mariachis when sober?

So you sojourn to Garibaldi, located in the historical center of Distrito Federal, and hand-pick a mariachi crew to follow you to your girl's house.

Uriel points toward one especially bold-looking guitarist, a burly dude in his 60s wearing a flattened mohawk and a tuxedo adorned with gold-threaded roosters. He says with gravity: "He's so… mariachi." It becomes our go-to adjective for the night.

I recruited Uriel not just because Garibaldi is increasingly seedy these days and my half brother carries himself like a Latin version of Ving Rhames, with his shirt unbuttoned to his gut and gold necklaces intermingling with his chest hair. No, I asked him to accompany me because, well, he's a man. Like most of us, he often finds he's just made a forehead-slapping mistake that requires a hastened, elaborate apology to his wife.

But he gets to atone with mariachis. As his stateside kin, meanwhile, I'm forced to try to make amends to my girlfriend with supermarket flowers and emoticon-laden text messages. I ask Uriel's wife why mariachi apologies work so well, even when he probably hires them for her three times a week. She just shrugs smugly, as if to say: You'll never understand, you sad, sad gringo. Why don't you go eat some Cheez-Its and watch Glee?

Uriel and I make our way to Salón Tenampa, the 80-plus-year-old heart of Garibaldi, where four competing bands rove for tips, and the walls are adorned with murals of historical mariachis so overgloriously depicted that they resemble Kim Jong Il-ish propaganda. Here, the traditional three-finger shot is more like three Lake Michigans. A few Cuba libres - the concoction of rum, Coke and soda water - and I'm feeling very, very mariachi.

The brand of Mexican folk music isn't only to express affection, Uriel tells me over the drinks, from what I can later decipher from the scrawls on my notepad. Mariachis also break out party anthems. Uriel nudges me and points out a peculiar scene beside El Tenampa's bar: a guy by himself, tilting with inebriation, holding his cell phone up to catch a love song being belted out by a mariachi crew he hired. Uriel shakes his head knowingly at what can only be described as the most budget of serenades. If there were an American equivalent, it would be bringing your date to stand outside the fence at a Justin Bieber concert.

But the real industry of Garibaldi relies on the beat-up band transporters - Chevy Astros, Ford Broncos, wood-paneled Chrysler station wagons - that idle around the square all morning, waiting to be dispatched to various love emergencies throughout the city. They may not have sirens atop their dented roofs, but they should.

We talk to a couple of the mariachis as they wait for jobs, and they tell us that the craft is passed down through sons. One old fellow named Ignacio Tobar, a dapper 70-year-old guitarist with perfectly coiffed white hair, says he's been snagging gigs at Garibaldi for 40 years. Then a call comes in and he leaps into the stuffed backseat of a station wagon with the rest of his band, headed to a neighborhood across town.

Delivering a van full of emergency mariachis for a set of songs is not cheap: It costs about $220. And in return, you earn forgiveness until the next time you screw up. Best fair deal in the country.