In the still of a snow-covered morning in upstate New York, a girl out riding her horse is hit by a 40-ton truck. Though horribly injured, both thirteen-year-old Grace Maclean and her horse Pilgrim survive. But the impact on their lives is devastating.

Grace's mother Annie hears about a man called Tom Booker, a 'whisperer' who is said to have the gift of healing troubled horses. Abandoning her job, Annie sets off across the continent with Grace and Pilgrim to find him. Under the massive Montana sky, all their lives are changed for ever.