MEXICAN STANDOFF By Bruce Cook Franklin Watts. 235 pp. $16.95

BRUCE COOK's mystery, Mexican Standoff, is a standout example of good genre fiction. "When the phone rang," the book says on the opening page, "I was half-awake, trying to persuade myself I was still asleep. Last night's Cuervo Gold had laid such a thick coat on my tongue that I could barely manage a hello . . ." The first thing that happens, then, is that the reader knows for sure what type of mystery this is -- hard-boiled, the kind that will feature a heavy-drinking, tough-talking, out-of-work private investigator. Right off the bat, then, Cook puts his book into a recognizable and immensely popular category. Cook, in effect, contracts with the reader, agreeing to satisfy certain conventions.

But that's not all that happens, because that's not all the reader wants. Within the familiar frame, the reader wants novelty, entertainment. What, the reader wants to know, is the twist, the spin, the elusive something that will make this mystery distinct from all the rest? Cook answers this question with his solid cast of characters and with some intriguing plot points, too.

This something-old, something-new dichotomy is what makes the creation of genre fiction more challenging than those who've never attempted it realize. It's comparable to, say, composing within a rigid and formulaic poetic form such as the sonnet or sestina. Done well, then, it is no mean feat. And here, in Mexican Standoff, it's done very well indeed.

The plot is tight, with hairpin turns and hairbreadth escapes. The action is almost nonstop. At the same time, there are plenty of laughs, plenty of near-slapstick scenes. There's a dose, too, of the macabre, involving, as the story does, hearses and embalmers and funeral homes and such.

Antonio Cervantes, the private eye, is introduced here as if he'll be around for many novels to come. That's excellent news. And I hope we can assume that Alicia, the prostitute who becomes his sidekick, will be present too. They are a formidable and very funny pair, good foils for each other. The chivalrous Cervantes is a former cop and he's gun shy. His weapon of choice in this book is a tranquilizer gun, the kind that puts animals in dreamland when they're being innoculated or moved to another part of the preserve. Alicia, however, is as tough as they come. In one scene she proves she has none of Cervantes' reservations and blows some corrupt Federales away. It is Antonio -- Tony, or better yet, Chico to his friends -- who has the heart of gold.

Much of the book takes place in the interior of Mexico, where Cervantes can put his Mexican-American background to good use. Cervantes is equally knowledgable about his homebase, Los Angeles ("On the freeway, you can feel the anger around you as though it were something physical. The slower the cars move, the higher the tension-level rises.") and the Mexican border towns, where the "U.S. greenback is the prevailing currency, and everybody there seems to be working some scam dedicated to accumulating as many as they can. You could call it a parasite economy . . ."

It is in a Mexican brothel that Cervantes and Alicia meet. Alicia, who wants to go to Hollywood so that she can be a movie star, often brings her acting talent into play, helping Cervantes out of scrapes. Prior to meeting him, she reminds him, she used it all the time, in bed. Aw, sure, all that is behind her now and after we hear how she fell into the life in the first place, we're a hundred percent on her side. She's a charmer, this girl who doesn't know a "Boorgoor Keeng" from a McDonald's and Chico is, understandably, far from immune. Beside, Chico Cervantes and Alicia Maria Ramirez y Sandoval are good together.

And there's plenty left in the relationship department for Cook to use. When Cervantes meets Alicia, for instance, and, indeed, when the book ends, she is with child. So even though this particular mystery concludes with no loose ends, we have a lot of imagined complications to look forward to in a sequel. The denouement here, by the way, is rousingly funny, especially because it relies on what had seemed throwaway material from an earlier scene. Hats off to Bruce Cook! :: Carolyn Banks' most recent book is "The Horse Lovers' Guide to Texas." She has also written several suspense novels.