IN THE PALM OF DARKNESS.<i> By Mayra Montero</i> .<i> Translated from the Spanish by Edith Grossman</i> .<i> HarperCollins: 192 pp., $21</i>

The frogs are going. By 1982, the Western toad had all but disappeared, victim--as if foretelling our own AIDS plague--of an immune system failure. In 1990, millions of frogs died in the ponds of northern Switzerland. That same year, the small golden frog of Costa Rica became extinct. A 1993 expedition to the Sierra Nevada in Colombia failed to find any remaining specimen of a luminescent black frog whose peculiarity was to freeze on cold days and revive on warm ones.

“You people invent excuses: acid rain, herbicides, deforestation. But the frogs are disappearing from places where none of that has happened.”

The speaker, in Mayra Montero’s novel, “In the Palm of Darkness,” is Dr. Emile Boukaka, a Haitian surgeon, frog expert and priest of a voodoo sect. To Victor, an American herpetologist searching for a rare frog in the Haitian mountains, Dr. Boukaka evokes Agwe Taroyo, god of waters, who has called the world’s frogs down to the sea bottom.

Victor mulls over the “you people.” Scientists, Boukaka means: “Fearful, finicky people, incapable of looking at the dark, recalcitrant, atemporal side of the decline.”

“In the Palm of Darkness” tells of Victor’s quest for the purple blood-frog, all but extinct, in the company of Thierry, an old Haitian guide. It is a metaphysical as well as a real expedition into the evil suggested by the title.

Montero, a Cuban-born writer, confronts the modern Western way of knowing with an older, more universal kind. Through the two men’s doomed endeavor, through Thierry’s tales and premonitions, and through Victor’s increasingly distraught brooding about his childhood and marriage, the reader is taken on a double journey.

The scientific rationalist encounters the irrational powers of voodoo and what begins to seem like its contemporary manifestation: the murderous brutality of the Tontons Macoutes. The Baron Samedi of the old rites dances crazily among the thug barons who use voodoo, as well as violence, to intimidate their victims.

It is a voyage into the heart of darkness. At the same time--as Victor’s frame of reference is invaded and an equivalent sense of evil bends the recollections of his life--it is a voyage into the heart of whiteness. Montero intends to pull down the wall between them.

In the frogs’ disappearance, there is no line to be drawn between modern ecological discoveries and the ancient god of the waters. Science elucidates forces it can’t deal with but, by its nature, it is unable to pay tribute to their mystery. Voodoo pays tribute to the mysteries without elucidating them. There is terror either way, though ours is more hidden.

Victor’s search has been commissioned by the world’s leading specialist in amphibians, an abstract old fanatic who can see nothing in life but frogs. To him, the Mont des Enfants Perdus (Mountain of Lost Children), near Port-au-Prince, is simply a reported blood-frog habitat.

Victor’s similar bias is soon subverted. The poverty of Haiti works upon him; so do Thierry’s whisperings about living dead, the zombies who prowl the hills and invade the villages. In fact, over starving generations, the boundary between living and dying has faded. Victor meets Haitians so thin that it is as if “their bones were trying to escape to find a better place to live.”

Thierry digs up a bone pile and zombie lore melds into an equally haunted reality. It is a warning, he says, to leave the mountain: Cito Francisque, a Tontons Macoutes chieftain, has reserved it for himself and his murdered victims. The warning is reinforced when their camp is trashed and excrement smeared on their belongings.

Later, Victor and Thierry attempt a second expedition, this one to a mountain on the other side of the island. There are warnings here too, and they are borne out when the guide of a plant biologist working on the same mountain is found dead, with his feet cut off.

The biologist, a woman, refuses to leave; “She will be dead tomorrow,” Thierry announces. He and Victor flee after capturing a last, ill blood-frog specimen. In a final understated passage--based on a real incident--the voodoo water god will, nevertheless, prevail over Victor and his illusory triumph.

Montero writes in an elaborate mesh of past and present, of natural and supernatural. The actions of Victor and Thierry fade in contrast with their ruminations and memories. In one section, each sentence of Thierry’s story about a promiscuous wife is followed by a sentence in which Victor thinks of his own wife, who left him for a woman. There is an equivalent unease and hollowness, a sense that the Earth’s crust is constantly giving way--through witchcraft in one case and, in the other, through an erosive contemporary system of values.

The author’s simultaneity of primal sorcery and modern agony are at their richest in Thierry. His father was a celebrated rural zombie hunter whose job was to track down the marauding creatures and destroy them. His corpse was discovered one day, skinned entirely. Whether the work of spirits or of real men, in Thierry’s story as in his life, there is no distinction.

He is an old man of sweetness and dignity, poetic and as subject to an indistinguishable hierarchy of human and magical forces--he was an occasional voodoo hit man and his brother belonged to the Tontons Macoutes--as the vanishing frogs. He speaks of lives and deaths, of women and wanderings.

Of his childhood in the town of Jeremie: “Haiti was a different place in those days. The sea was wider or deeper or more loved by the fish.” And when Victor weeps suddenly, afflicted by the memory of his wife--which takes on the estranging spookiness of his surroundings--Thierry draws from his own sorrows: “A man never knows when the grief begins that will last forever.”

By contrast, Victor is drawn more uncertainly and arbitrarily. Showing the frailty of the barriers between modern society and a primal, magical notion of evil--all the frailer because the modern evil is unacknowledged--Montero over-contaminates him. He is so odd and undone from the beginning that he implies little reality of his own. Montero’s parable is one-legged--gorgeously, but even so, it has a limp.