Nine-year-old Tory has been bumped from foster home to foster home. Living with a foster family on a horse ranch for the summer, she falls in love with Lucky, the shaggy pony she is allowed to ride. When a nearby forest fire forces the family to evacuate, Tory is devastated when Lucky has to be left behind. The story alternates between the points of view of Lucky and Tory. Lucky flees from the fire into the wilderness, where he searches for water and faces various dangers, including a brush with wolves and a tangle with barbed wire. Eventually Lucky finds his way to Rainbow Ranch, the home of a kind couple and their foster son, Patrick, who doesn't speak.
Meanwhile, Tory's life seems full of problems, including worrying about Lucky, trying to control her temper and wondering where she'll live next. When she finally tracks Lucky to Rainbow Ranch, she makes the difficult decision to leave him in his new home with Patrick. Tory's selflessness and understanding may lead to her finding a home at Rainbow Ranch as well.