Lon McCallister is the wayward young lad "Sparky" who is sent to live with his aunt "Penny" (Charlotte Greenwood) and uncle "Thunder" (Walter Brennan) in rural Indiana. Instead of going to school each day, he manages to find work at the neighbouring stud farm where he shows considerable skill with the animals. His uncle also has past with horses, so after a bit of a rocky start they all start to bond - and to train one of the horses to race, trap style. The horse is owned by the "Boole" family who have a daughter, the slightly superior "Cri-Cri" (June Haver) who is friends with the daughter of ...