Formula fiction, like franchised fast food, is predictable. Buyers know just what they're getting. Alan Cochran's "Two Plus Two" follows the whodunit recipe (the plot: when three club members are murdered, a male-female cop team goes undercover to find the murderer) right down to the last pickle chip . . . but, oh, that special sauce! m

The victims, you see, aren't members of a church choir or a gardening group. They're swingers, and Two Plus Two is the private club where they swap partners and more. And Cochran doesn't leave us to imagine the goings on. His cops, Jason Price and Brooke Merritt, get right into the thick of it. The resulting book is so bawdy that formula-mystery readers may well start to squirm.

Much of "Two Plus Two," however, is very funny. Caricatures abound. There's Jim, who runs the club, and who talks about it in dissertationese, speaking of those who "have successfully come to terms with the basic reality gestalt of swinging, and are prepared to enter the realm of full potentiality awareness beyond ego fulfillment." There's Cassie, the most direct third-grade teacher we'll ever meet. And Rick, and Eric, and Franklin, all very well drawn comic types.

Situations, too, are milked for their comic potential: When Jason attempts to revive a women who's overdosed on drugs, giving mouth-to-mouth resuscitation, the bouncer stops him, assuming the worst. "We don't play that way here," the bouncer says.

Jason Price, too, is a type: the wisecracking narrator-hero whose perceptions are sharp (his five-word assessment of the girls who advertise in sleazy classified is "Tina, Rena, Lola, Trina, Darla") and decidedly Californian ("What we'd come to was one of those sprawling, pseudo-Spanish type mansions that you associated with aging movie stars or new rock groups"). He is, refreshingly, a beer snob, telling us throughout of the merits of little-known brews like Leopard (from New Zealand) or Amarit (a Thai lager) or St. Pauli Girl. When the going gets rough, though, Jason drinks Jack Daniels.

When the going in "Two Plus Two" gets rough -- that is, when the book seems to be slipping out of the mystery slot and into porn, Cochran redeems it with Jason's moral indignation, which the reader is invited to share:

"Some modern dude I was. About as liberated as King Kong. But goddammit, what did that have to do with liberation -- watching the woman you were with strip off her clothes and make it with some stranger, and in front of fifty other strangers, no less? Didn't that qualify for some kind of new low mark in cuckoldry?"

This gets everybody -- author Alan Cochran, narrator Jason Price, and us -- off the hook. It provides a built-in Tsk! to accompany description fuller and freer than it might otherwise be.

But the effect is only temporary. When we move out of the club and into the Bel Air suburbs, it seems that Cochran has lost control of his book -- or perhaps has changed his emphasis. At any rate, the situation is raunchier than any ever to appear in a mystery and Cochran -- perhaps distracted by all that heavy breathing -- lets slide the perfect opportunity to bring the chapter home. He could have done this handily in the scene where Brooke was ordered to choose a partner and have sex with that person in a way she had never done before. What a marvelous chance to continue the burlesque -- except that Cochran doesn't, and we cannot help but wonder why.

Thus "Two Plus Two" is a book which will require defense. Had this chapter been handled differently, it would have been possible to say that sex is to "Two Plus Two" as food was to "Someone Is Killing the Great Chefs of Europe." All and nothing. But no matter. Those readily offended will have stopped reading long before this, and anyway, when the murderer is revealed, the motive is so perfectly ironic, we forgive Cochran his lapse.

Alan Cochran, according to Publishers Weekly, is a pseudonym, which has us wondering if the author's real name might not be Gay Talese. Much of the material in this book -- including sidelights on swinging overseas -- could be leftovers from "Thy Neighbor's Wife," also published by Doubleday.

But perhaps not, because the flap copy hints that "Two Plus Two" is the start of a series featuring the LAPD pair, Jason and Brooke, who are in love with each other by the book's close.