Willy and his grandfather live on a farm in Wyoming where they grow potatoes. One day Grandfather will not get out of bed or even speak. Willy runs to get Doc Smith, who examines Grandfather and can find nothing wrong with him. She tells Willy that Grandfather has just given up on life.
Willy brings in the potato harvest to cheer Grandfather, using only his dog, Searchlight, to pull the plow. He is able to sell the potato harvest just as Grandfather has always done, but still Grandfather does not move or speak.
Each winter Willy hooks Searchlight up to an old sled and, daily, they race the distance from their farm to town and back again. One winter day, he returns home to find a 'city slicker' at the farm. The man says he is from the State of Wyoming, and tells Willy that Grandfather owes the state $500 in back taxes, and that he must pay it or they will lose the farm.
Then, when Willy goes to town, he sees a poster advertising the National Dogsled Races. The for winning the race is $500! Willy decides to enter the race, convinced he and Searchlight can win; but an Indian named Stone Fox also enters the race. Stone Fox has never lost a race. Can Willy and Searchlight beat Stone Fox?