Bernard (Bob Newhart) and Miss Bianca (Eva Gabor), two New York City mice, are members of the Rescue Aid Society, an international team that operates beneath the United Nations and comes to the aid of those in need. After receiving word that Penny (Michelle Stacy), a young orphan, has been abducted by Madame Medusa (Geraldine Page), an evil woman seeking a precious diamond, the two set out to bring her back home, with help from other animal friends.