Mrs. Frisby is the protagonist of the story. Her character growth is fuelled by her courage and willingness to do whatever is necessary to protect her family. Mrs. Frisby is a field mouse whose husband Jonathan died the summer before. She has been left with four children to care for and is still in the throes of grief when the winter is ending in late February as the story begins. Mrs. Frisby’s actions are guided by the memory of her husband and her love for her children. She thinks of Jonathan often, remembering the ways he used to comfort his children, share his knowledge of reading and other interesting things, and how devoted he was to his family. When Mrs. Frisby’s youngest son Timothy becomes ill with pneumonia, she takes it upon herself to find a solution both to his illness and to the predicament surrounding moving her house. Mrs. Frisby recalls “something her husband, Mr. Frisby, used to say: All doors are hard to unlock until you have the key. All right. She must try to find the key. But where? Whom to ask?” (30).

When the story begins, Mrs. Frisby is a fairly typical and timid field mouse.