Darby is an old widower who lives with his daughter, Katie (Janet Munro), as groundskeeper on the country estate of Lord Fitzpatrick. Darby spends most of his time loafing, poaching the very rabbits he is supposed to be protecting from poachers, and telling tall tales at the pub of his adventures with the little people, leprechauns. Darby once caught the king of the leprechauns and got 3 wishes. However, the king offered him a 4th wish out of "kindness" to Darby. Once Darby makes a 4th wish, the king reveals that if you make a 4th wish it nulifies all the other wishes, so Darby loses everything.
Lord Fitzpatrick is fond of Darby but has had enough. He fires Darby and brings in Michael McBride (Sean Connery) to replace him. Darby and Katie will have to move off.
Darby gets Lord Fitzpatrick and Michael to agree to give him 2 weeks to break the news to Katie, during which Michael will pretend to be Darby's assistant. Darby's secret plan is for Michael and Katie to fall in love and marry, so all can stay together on the country estate.
Darby catches the leprechaun king again, and decides that this time he will hold on to the king for a while to make sure he gets good use of his wishes. He keeps the king in a burlap sack and carries him around with him everywhere.
For 1 wish, Darby sees the secret underground home of the little people. Katie gets very sick and the coach of death comes for her. Darby tries to use his last wish to send the coach of death away. The king tells him it is beyond his powers, the coach can not return empty but must have someone in it. Darby wishes for the coach to take him instead. The king grants this sadly, as he respects and is fond of his old adversary Darby. The king comes along with Darby for the ride in the coach. As the coach nears its destination, Darby makes a 4th with. With the 4th wish, all the wishes are nullified, and Darby is no longer in the coach but is back home. It is too late for the coach to turn around .
Katie recovers. As Darby planned, she and Michael fall in love, and they all live happily ever after.