By Kem Nunn

Scribner. 306 pp. $25

Good novels are hard to categorize. The publisher calls Kem Nunn's "Tijuana Straits" both "violent beach-noir" and "a literary surfer thriller," and there's truth as well as hype in that, but it is also in part a political novel. More broadly, it belongs to the great tradition of books and movies in which a high-minded woman enlists a cynical, reluctant man in some cause that is hers, not his. Thus was Humphrey Bogart twice persuaded to take up arms against the Nazis, by Ingrid Bergman in "Casablanca" and by Katharine Hepburn in "The African Queen," and I seem to recall John Wayne and Clint Eastwood being similarly seduced in other films. In "Tijuana Straits" the crusading woman is a Mexican political activist named Magdalena Rivera, and her unlikely savior is a grizzled ex-surfer, ex-drug runner and ex-convict called Sam (the Dove) Fahey. The world they inhabit extends from her Tijuana to his worm farm, just across the border in the California no man's land of the Tijuana River Valley, and Nunn makes it abundantly clear that this desolate wasteland of smugglers, bandits, illegal immigrants, exploited workers and burned-out hippies is hell on Earth.

When Magdalena was a child, she and her mother lived in a border shantytown that the Mexican government wanted for development. When the occupants fought back, the government opened the floodgates of a dam and drowned 100 people, including her mother and grandmother. The child was raised and well educated in a Catholic orphanage, and when we meet her she is a 23-year-old activist who works for a lawyer, volunteers in a women's shelter and is gathering information about pollution, corruption and cruel working conditions. "She sometimes thought of the foreign-owned factories as the parts of some monstrous organism dropped from the heavens, settling its tentacles into the arid ground, reaching deep into the heart of her country. With the advent of NAFTA, the monster had grown stronger and fatter, with more factories, more pollution, greater abuse of the workers -- the very things she had come to fight, in her mother's name, in the name of the planet."

Early in the novel, someone tries to kill Magdalena, and she flees, battered and half-dead, across the border where the forty-something Fahey rescues her. He takes her to the shack where he drinks a great deal of beer, listens to Chet Baker recordings and cultivates his "herd" of night crawlers. He is a bearded, long-haired, shambling wreck of a man -- think Nick Nolte 20 years ago -- who was once a legendary surfer. Now, after two prison terms totaling some six years, he seeks only peace and solitude. He can't remember the last time he had a woman. Despite his solitary nature, he nurses Magdalena back to health, treats her with respect and lets her persuade him to cross the border to Tijuana to claim the precious files she thinks will bring down the polluters and corrupt officials of her government.

The third major character in the novel is a quite horrific villain named Armando, but Nunn shows us that this monster is himself a victim of the world he inhabits. Armando grew up in poverty in Mexico City and went to Tijuana to pursue his dream of becoming a boxer. Instead he wound up working in an American-owned factory where he glued leather covers onto automobile steering wheels. "He could do forty wheels a day, for which he was paid two dollars and sixty-nine cents." He and the other workers spent all day inhaling the fumes from the glue and other toxic materials, which poisoned their bodies and damaged their minds. Armando married, and his wife had a child, but it was born deformed and died. This, he learns, is a common occurrence among the factory workers, but plant officials assured him that his child's deformity was "a part of nature."

Armando is fired, his wife leaves him and he finds work as a strong-arm man for the drug lords. Along the way, he invades the women's shelter where his wife has taken refuge, sees Magdalena and becomes convinced that she is a witch who has destroyed his dream of having another child. It is the crazed Armando who tries to kill Magdalena at the start of the book, and when she escapes he and an equally lethal partner track her down at Sam Fahey's home across the border in California. The climax of the novel is a long, suspenseful scene in which Fahey struggles to save Magdalena from the killers.

Kem Nunn, a third-generation Californian, is a fine stylist who knows a great deal not only about surfing but also about life along the border, working conditions in Tijuana, lives of violence and the joys and pitfalls of drugs.

He ends this novel, his fifth, in a surprising manner. After the outcome of the clash with the killers, he adds a kind of epilogue about surfing. Throughout the book, there has been talk of the Mystic Peak, the great mountain of a wave that may emerge only every 10 years and can be conquered only by the greatest surfers. Now, finally, one arrives to challenge Sam Fahey in the twilight of his career. I'm not sure this episode really belongs in the novel, but it is clearly Nunn's intention that Sam Fahey not simply be the hero of a thriller but should assume the status of a mythic figure. I think he succeeds. If there is a literature of surfing, "Tijuana Straits" is surely one of its classics. Among other things.