Their father, a powerful business man (Jack Scalia from 'Tall, Dark & Deadly' and 'The Silencers') is to remarry and sends the children to Ireland to spend the summer with his intended, a woman they have never met.
Once in Ireland, the children quickly grow to dislike the woman, Laura Duvanne (played by Veronica Hamel of 'Hill Street Blues' and 'Filofax' fame). Their worst nightmare is realised when they discover her to actually be an evil, power seeking water banshee with real magical powers and a hatred for all things green.
With the aid of her loyal butler (David Warner from 'Titanic' and 'Time Bandits'), Laura plans to flood the forest and drown its Keeper, Fin Rigan McCool, the last King of the Leprechauns.
Ethel and Tommy find an ally in Mary (Laura's housekeeper) and so they join forces with the Leprechaun to defeat Laura's evil scheme.
As they unite in their fight against this evil witch, the children come to understand their father, his aloofness and the reason for his absences. In the process, they even manage to cultivate a romance between Mary and their father and so create a chance to have a normal family life.
This is an enchanting story of magic and family loyalty, good over evil and most importantly, of the dreams and determination of lonely children who want to be loved.