Book excerpt: Yellowstone National Park's majestic geologic wonders and remarkable wildlife draw millions of visitors each year. But there was a time when these natural treasures were in great danger, all because after years of unrestricted hunting, one key piece of the puzzle had been eliminated—the wolf. Now, more than a decade after scientists realized the wolves' essential role and returned them to Yellowstone, the park's natural balance is gradually being restored. The informative dual-level text and spectacular full-color photographs show the wolves in the natural habitat that was almost lost without them. Readers of all ages will be inspired by the delicate natural system that is Yellowstone.