Mrs. Frisby, a widowed mouse who lives in Farmer Fitzgibbon's vegetable garder with her four children, is at wit's end. Every year when the cold weather passes into springtime, Mrs. Frisby moves her family to their summer house in the pasture by the stream. But this year there is a problem: Timothy, her youngest son, has pneumonia, and is far too weak to make the yearly move. And Mrs. Frisby just overheard Farmer Fitzgibbon telling his sons that he would begin plowing in five days. In five days her family's winter home will be completely destroyed, and they along with it. She's tried everything she can think of. Should she take the owl's advice and ask for help from the brilliant rats of NIMH?