On a hot August day in the 1880s, at the Ingalls' homestead in Dakota Territory, Laura offers to help Pa stack hay to feed their stock in the winter. As they work, she notices a muskrat den in the nearby Big Slough. Upon inspecting it, Pa notes that its walls are the thickest he has ever seen and fears the upcoming winter will be a hard one.

In mid-October, the Ingalls wake to an unusually early blizzard howling around their poorly insulated claim shanty. Soon afterward, Pa receives another warning from an unexpected source: an old Native American man comes to the general store in town to warn the white settlers that there will be seven months of blizzards. Pa decides to move his family into his store building in town for the winter.

In town, Laura attends school with her younger sister, Carrie, until the weather becomes too unpredictable to permit them to walk to and from the school building, and coal too scarce to keep it heated. Blizzard after blizzard sweeps through the town over the next few months. Food and fuel become scarce and expensive, as the town depends on the railroad to bring supplies but the frequent blizzards prevent trains from getting through. Eventually, the railroad company suspends all efforts to dig out the trains that are snowed in at Tracy, stranding the town until spring.

With no more coal or wood, the Ingalls learn to use twisted hay for fuel. For weeks, they subsist on just a little bit of food. As even this meager food runs out, Laura's future husband, Almanzo Wilder, and his friend, Cap Garland, hear rumors that a settler raised wheat at a claim twenty miles from town. They risk their lives to bring sixty bushels of it to the starving townspeople – enough to last the rest of the winter.

As predicted, the blizzards continue for seven months. Finally, the spring thaw comes and trains begin running again, bringing the Ingalls their long-delayed Christmas barrel from Reverend Alden, containing clothes, presents, and a Christmas turkey. With the long winter finally over, they enjoy their long-delayed Christmas celebration in May.