Mrs. Frisby is the widowed head of a family of field mice. Mrs. Frisby's son, Timothy, is ill with pneumonia just as the farmer Mr. Fitzgibbon begins preparation for spring plowing in the garden where the Frisby family lives. Normally she would move her family, but Timothy would not survive the cold trip to their summer home. Mrs. Frisby obtains medicine from her friend Mr. Ages, an older white mouse. On the return journey, she saves the life of Jeremy, a young crow, from Dragon, the farmer's cat - the same cat who had killed her husband, Jonathan. Jeremy suggests she seek help in moving Timothy from an owl who dwells in the forest. Jeremy flies Mrs. Frisby to the owl's tree, but the owl says he can't help until he finds out that she is the widow of Jonathan Frisby. He suggests that Mrs. Frisby seek help from the rats who live in a rosebush near her.