Mrs. Brisby, a timid widowed field mouse, lives in a cinder block with her children in a field on the Fitzgibbons' farm. She prepares to move her family out of the field as plowing time approaches, but her son Timothy has fallen ill. She visits Mr. Ages, another mouse and friend of her late husband, Jonathan, who diagnoses Timothy with pneumonia and provides her with medicine. Mr. Ages warns her that Timothy must stay inside for at least three weeks or he will die. On her way home, she encounters Jeremy, a clumsy but friendly crow. They both narrowly escape from the Fitzgibbons' cat, Dragon.