Nine-year-old Kaylee Winkles has always dreamed of having her own horse. Her parents, however, say she's just not old enough for a horse of her own. One night, a terrible storm erupts over the ranch where Kaylee lives, and in its aftermath, she finds a mysterious guest: a tiny horse. A baby unicorn, the last of her kind, and in great danger from a dark force whose only goal is to imprison the unicorn and hide her from the world. With the help of her family, Kaylee must stand up to the evil that would lock away the unicorn and defeat the darkness before it overtakes the light.