Tommy and Ethel Barridge, the children of multi-millionaire American business man Henry Barridge, go to Ireland to spend the summer holidays with Laura Duvall, who is engaged to marry their father. However, they find she is a wicked banshee with strong black magic powers who does not wish them well. Laura is busy cutting down trees on her estate and is also planning the destruction of the last king of the little people, or leprechauns. Tommy and Ethel take his side against their wicked future stepmother.