When a bottle containing a plea for help from a little girl named Penny makes its way to the Rescue Aid Society, a mouse organization in the basement of the United Nations building dedicated to the rescue and well-being of anyone in need, it is up to the brave mouse Miss Bianca and her chosen partner, the shy janitor Bernard to rescue the girl. Searching for clues at her home at Morningside Orphanage in New York City, the two mice discover that the girl has been kidnapped by the evil pawn shop owner Madame Medusa and her companion Mr. Snoops. On the back of Orville the albatross, Miss Bianca and Bernard travel to the terrifyingly gloomy Devils Bayou island where they learn the shocking truth: The innocent young girl is being forced down into a dangerous, dark underground pirates cave where she must find the Devils Eye, the worlds largest diamond and Madame Medusas greatest obsession...