Lucy, a highly intelligent cat, discovers Betty, a young castaway, on the shores of their island and brings her back to the home of her owner, Mammy Blue. Mammy takes care of Betty and, with the help of Doctor Platini, the strange inventor, sets out to find out who the little girl is so she can safely return her to her family. Betty steals the hearts of the inhabitants of the island, even the most difficult ones. Along with her new friend, clumsy Eric, they try to solve the mystery of the shipwreck, ignoring all dangers including the terrible pirate Redbeard, who suddenly sets foot on the island awakening the inhabitants' worst nightmares. Will Lucy be able to come to her friend's aid?