Lucky Prescott never really knew her late mother, Milagro Navarro, a fearless horse-riding stunt performer from Miradero, a small town on the edge of the wide-open frontier.

Like her mother, Lucky isn't exactly a fan of rules and restrictions, which has caused her Aunt Cora no small amount of worry. Lucky has grown up in an East Coast city under Cora's watchful eye, but when Lucky presses her own luck with one too many risky escapades, Cora picks up stakes and moves them both back with Lucky's father.

Lucky is a fish out of water in the raucous railroad town, but she has a change of heart when she meets Spirit, a wild Mustang who shares her independent streak, and befriends two local horseback riders.

When a heartless horse wrangler and his team capture Spirit and his herd and plan to auction them off to a life of captivity and hard labor, Lucky enlists her new friends to stop them. Together, the girls bravely embark on the adventure of a lifetime to rescue the horse who has given Lucky freedom
and a sense of purpose and has helped her discover a connection to her mother's legacy and to her Mexican heritage that she never expected.