"The Great Horse" is adapted from a true story. Penny Chenery (Diane Lane) was originally an ordinary housewife. She knew almost nothing about horse racing, but she took over the horse farm in Virginia from her sick father amid the opposition of her brother and husband. Although the horse farm had been losing money for a long time, she still had to run back and forth between Colorado, where she lived, and Virginia, where the horse farm was located. In order to find a good horse, Penny specially found the retired horse trainer Lucien (John Malkovich), who always complained a lot, but treated the layman Penny differently. Penny fell in love with a chestnut pony in the horse farm that could stand up after rolling at birth, and named it "Secretary". Under Lucien's personality training, "Secretary" made a splash when he first came out. It is as fast as lightning, leaping like a flying horse, like a warrior, and even excited by the vibration of the ground in the stadium. Finally, it's time to decide who wins and who loses. Will Secretary withstand all the pressure, live up to Penny's expectations, and become the first horse to win the American Triple Crown in 25 years?