The further adventures of the intelligent young rat Racso and his friends Christopher and Isabella as they try to ensure the survival of their secret community in Thorn Valley after its accidental discovery by two human children.

Having no one to help her with her problems, a widowed mouse visits the rats whose former imprisonment in a laboratory made them wise and long lived. Mrs. Frisby, a widowed mouse with four small children, is faced with a terrible problem. She must move her family to their summer quarters immediately, or face almost certain death. But her youngest son, Timothy, lies ill with pneumonia and must not be moved. Fortunately, she encounters the rats of NIMH,...