The Great Dan Patch (movie, 1949)

David Palmer, a young chemist, returns to his father's Indiana farm, to marry a local school teacher, Ruth Treadwell. David meets again his father's horse-trainer, Ben Lathrop, whose daughter, Cissy, has left high school to help her father. Palmer marries and becomes wealthy through an invention, and is able to indulge his socially-ambitious wife. His father dies and Palmer returns to Indiana, where his interest in harness-racing is rekindled, as is his interest in Cissy Lathrop.