The Landon family has come to Montana's Glacier National Park to help figure out why grizzly cubs are disappearing. But for 12-year-old Jack, the real mystery is his sister Ashley's strange behavior. What was she doing in the woods alone so early in the morning? And why did she lie to their parents? A chain of heart-pounding events bring Jack and Ashley face-to-face with an enraged mama grizzly, and they find themselves running for their lives as they become the hunted.