As Orson Welles knew, border towns are spiced with a touch of evil. They are nebulous nether regions where allegiances are shady and the rules change within the space of a dozen yards. Tex-Mex, the cuisine born of that uneasy schizophrenia, retains some of the intrigue of its homeland. Few innocent consumers should be bamboozled into believing, for example, that the stale tortilla coated with brown paste and overflowing with sour cream and jack cheese might with pride be called a burrito, or that the proper recipe for guacamole calls for mayonnaise. Just as Hank Quinlan--the crooked cop Welles plays in his recently re-released film noir--might have done in their shoes, they are better served drowning the lot in hyper-colored treacly margaritas served in icy troughs.

Sadly, the empty tables at Baja Mexican Cantina do not testify to the fact that it succeeds where Harvard Square's Border Cafe fails. Perhaps this is in reality another nod in Baja's favor. Located in the increasingly yuppified South End, Baja benefits from decor that is unabrasively funky. The windows and the bar are framed by red plastic chile lights, sombreros grace the walls and bright green cactus sculptures are sunk into cavities in the walls. Triangular flags pushing tequila brands are a tribute to kitsch, but the gestalt works well, set off under a trendy corrugated tin roof. The TV at one end of the bar and the gravelly sound of Louis Armstrong add to the user-friendly feel. In addition to comfortable surroundings, Baja offers many weekly specials that ought to bring in the crowds: a Sunday all-you-can-eat buffet for $8.95, and happy hour from 4 to 7 pm Sunday to Tuesday features half-price appetizers and free nachos.

Appetizers include Tex-Mex standbys like nachos, guacamole and chorizo-studded queso-fundido. However, a few more innovative twists and flair, such as spicy Aztec soup ($2.95), with its thick tomato base brimming with onions, corn, chile and lime, topped with strips of tortilla chips. Smoky Avocado Chipotle Salsa ($3.95) resembles a cross between salsa and chunky guacamole, served with Tostones, which are fried plantain chips. Peel-N-Eat shrimp ($6.95) are an even more unusual addition to a Tex-Mex menu, served with spicy cocktail sauce and a side of salsa fresca. For grease-craving grazers, the Baja Sampler ioffers a medley of deep-fried jalapenos stuffed with cream cheese, chile chicken wings, a vegetarian tamale, and guacamole and chips.

Like the appetizers, entrees embrace the traditional and the atypical alike. Even the often prosaic burrito exceeds expectations, however, laced elegantly with chile sauce, stuffed with grilled salmon, whole black beans, and brown rice and served on a bed of shredded lettuce and salsa fresca ($10.95). Grilled catfish ($10.95) is crusted in cornmeal and rests on a bed of rice pilaf, accompanied by a salad whose dressing is vaguely reminiscent of peanut sauce. The dish holds together well as a lighter option that remains flavorful and coherent. Chile rellenos ($9.95) sound unusual as well, advertised as Anaheim and Poblano peppers stuffed with shredded chicken, cheese, sun-dried tomato and pumpkin puree, a combination that dares to depart from the norm. Baja also creates an entirely new form of fusion, a Mexican-style pizza with a tortilla crust, covered by black bean puree, and a selection of toppings ranging from grilled anaheim peppers, grilled corn and jack cheese to spicy ground beef with enchilada sauce or charred vegetables with queso blanco and ranchero sauce ($5.95).

As a necessary prerequisite for any Tex-Mex restaurant, Baja offers a wild assortment of margaritas, both standard and bastardized with the likes of Chambord and Grand Marnier. A timely cantina, the bar also offers two martini specials: Fuzzy Grape Chinaco Martini (Chinaco, Peach Schnapps, grape juice and sour mix) and Tarantula Martini (Tarantula Azul, Cointreau, and Chambord). The mere descriptions sent my insulin levels through the roof and the floor at once.

For the hard-core elite who prevail undaunted over large portions and head-swimming margaritas, dessert is a necessary evil. Chocolate Ecstasy is a towering mound of stratified richness--cream, chocolate mouse and chocolate cake soaked in kahlua--alluring enough to be devoured in spite of flagging spirits. Coconut flan sounds interesting, and for a palate cleansing option, Baja offers Key Lime Tart, a denser version of the more common Key Lime Pie.

Baja provides a menu that can appeal to all sorts--timid Tex-Mex neophytes may content themselves with their nachos and their quesadillas, while those with creative spirits may expand their horizons with pumpkin-stuffed rellenos or tortilla pie with chile mashed potatoes. Ingredients taste fresh, service is quick and friendly, and the wait on a Monday night was nonexistent. The Border was happily bypassed, and can remain forever ensconced in the shadow of a superior eatery across the river.