Dennis Drabelle is a contributing editor of Book World.

The Last Unicorn
A Search for One of Earth’s Rarest Creatures

By William deBuys

Little, Brown. 354 pp. $27

One night in camp, the author of this book asks an American expert on South Asian wildlife, “How do you maintain optimism?”

Answer: “What makes you sure I do?”

‘The Last Unicorn: A Search for One of Earth's Rarest Creatures’ by William DeBuys (Little, Brown)

That exchange comes about midway in “The Last Unicorn,” William deBuys’s gripping and stylish account of a trek he went on four years ago to the remote Annamite Mountains of Laos, flush against the Vietnamese border, in search of the saola. A three-foot-tall, forest-dwelling animal that resembles a deer but belongs to a genus all its own, the saola was unknown to Western scientists until 1992, and two decades later its continued existence was in doubt. Since it has a pair of swept-back horns, the animal’s similarity to the unicorn is purely metaphorical — what the two creatures have in common is their elusiveness.

DeBuys’s question to the expert, biologist William Robichaud, was prompted by signs that Vietnamese poachers were crossing the border and trapping various animals to harvest their parts — especially horns and hooves — valued by practitioners of folk medicine. (DeBuys argues that they might as well use parings from a human fingernail, which has the same medicinal value — none — as an antelope’s hoof or a rhino’s horn. All three are made of the same substance, keratin.)

These encroachments should not have been happening. In return for World Bank funding of a massive hydroelectric project, the Laotian Watershed Management and Protection Authority had promised to patrol the region assiduously. But as shown by the welters of ensnared and rotting animal carcasses along the trails, “the WMPA’s enforcement of prohibitions against hunting and trapping by outsiders has so far proved notoriously ineffective.” Indeed, the legendary George Schaller — the wildlife biologist who accompanied writer Peter Matthiessen on his quest for the snow leopard four decades ago — refused to work in Laos anymore. “The government is not serious about conservation,” Schaller complained.

Whenever they came upon a poachers’ camp, deBuys and company took a kind of frat-boy glee in trashing the place and confiscating every snare within sight. But they knew that the Vietnamese could return and rebuild with impunity if they chose to.

The trek was arduous — steep, slippery trails with multiple water crossings — and all members of the party, not just the porters, had to tote heavy loads. Meanwhile, the tropical landscape was crawling with hazards. Here is deBuys describing a representative stretch of downhill hiking: “Reaching out to steady myself and check my momentum, I realize, too late, that the slender trunk I am about to grab bristles with thorns. At the point of falling, I lunge for a different sapling, a different shade of bark, surely a safe one — and sink my hand into a living skin of ants.”

Other complications were introduced by the porters. Early on, some of them would stay up and cook themselves a second meal after Robichaud and deBuys turned in for the night. This wreaked havoc with the meticulous rationing calculated by Robichaud to get the group through the trip with enough to eat. One porter in particular was by turns obsequious and sullen — and a thief who pilfered from others’ packs. DeBuys sums him up as a “human toothache.”

DeBuys is an evocative writer. Here he is noting the rapid arrival of the tropical sunset: “Close to the equator, night descends like a curtain in a theater. There is no leisure in the sunset. One minute you bask in yellow light, the next you barely see your hand.” Recalling a visit to a dying friend back home in New Mexico, deBuys writes: “To hug her was to feel a spine like a blade and a back paved in bone.” Fancifully, he speaks of the saola in terms of quantum physics: “They are the quarks of the wild world, particles so small and fleeting that they defy our powers of seeing and measuring. We know them better in theory than we do in fact.”

The prognosis for the saola and the rhino and the tiger and many more wild Asian species is not good. “About half the world’s people live in Southeast Asia or the adjacent countries of China, Bangladesh, and India,” deBuys writes. “Southeast Asia (including Indonesia and the Philippines) leads the rest of the world in the proportion of its birds and mammals that are found nowhere else. It also leads the world in the proportion of its biota in grave, current danger of extinction. No part of the region has a tradition of effective biological conservation.” As he notes a few pages later, “To care about the world, we have to open our hearts, but by opening them, we make them easier to break.”

Then, after the expedition is over, come glimmers of hope. Robichaud’s report on extensive poaching in the Annamites spurs the WMPA to take its responsibilities more seriously. And in September 2013, a camera set up in Vietnam captures a wild saola on film. The last unicorn still has a tenuous purchase on life, and it’s just possible that deBuys’s heartfelt pleas will make a difference.