This year's summer holidays are going to be very different for Ethel and Tommy Barridge. Their father, a powerful businessman (Jack Scalia) is remarrying and he is sending them to Ireland to spend the summer with his fiancée, who they have never met. Their worst nightmare is realized when they discover that their future step mother, Laura Duvann (Veronica Hamel) is actually an evil, power-seeking water banshee with real magical powers and a hatred for all things green. With the aid of her loyal buder (David Warner), Laura plans to flood the local forest and drown its keeper, Finn Regan McCool, the last King of the Leprechauns. It is up to Ethel and Tommy, with the help of the Leprechaun, to thwart Laura's evil scheme.