Amy is startled when her enemy, Ashley Grant, arrives at Heartland looking for someone to train her horse, Bright Magic, but after taking on the responsibility and working closely with Ashley, Amy finds herself warming up to the girl.

The flu has overrun the horses at Heartland, and despite Amy and Ty's efforts to keep the unaffected horses out of risk, the illness keeps spreading, and causes a rift in friendships.

Already struggling to keep up with the chores at Heartland and maintain a positive outlook while Ty is in the hospital, Amy is challenged in every way by the wild mustang that defies her attempts to reach out to him.

Amy's mother founded Heartland, a place for healing traumatized horses, but Amy, who inherited her mother's skills with horses, must continue her work after an accident on a stormy night kills her mother.

On a visit to their father's ranch in Australia, Lou has no difficulty accepting her father's new wife, Helena, while Amy seeks refuge in the stables and in working with Spirit, the reluctant grey gelding trained by Helena.