IN OLD KENTUCKY, there were two feuding families, the Martingales and the Shattucks. Steve Tapley (Will Rogers), a horse trainer, gets caught up in that feud and takes sides - specifically, that of beautiful young Nancy Martingale and Ezra, her grandfather. It is decided that the feud will be settled by a horse race. However, Greyboy, the favored horse of the Martingales, is a mudder - in other words, he can only run well in soft, muddy ground. And there's been a bit of a drought lately