When the howl of a wolf is heard in fairy tales, the villagers close the door with all four buttons. They watch anxiously for the flash of yellow eyes in the darkness. And yet some say that there is a wild, untamed magic in the voice of the hunting pack.

For hundreds of years, wolves were the rulers of Yellowstone. They circled their territory, tirelessly following the wapiti deer. But over time, people came here and started killing. The wolf tracks disappeared without a trace. The wailing of the puppies as they learned to swim in the rivers and streams ceased.

When the wolves disappeared from the national park by poachers, hunters and ranchers, the wapiti deer population grew excessively and threatened many plant species. Some birds flew away in search of new habitats. Even the bears were starving. Fortunately, thanks to the determination and persistence of ecologists, a system of reintroduction of the species was created and in the winter of 1995, a dozen Canadian wolves found their way to Yellowstone. Catherine Barr, who relates their fate, talks in a fascinating way about interdependencies in the natural world. It proves that predators are indispensable in the ecosystem, and shows how man (out of ignorance, selfishness or fear) upsets the fragile balance of the planet.