Grandpa Ward, a Traveller, is followed from the beach to his Ballymun encampment by an enormous white horse. There he encouters his son-in-law, Papa Riley, once king of the Travellers but since the death of his wife (Grandpa's daughter) giving birth to their second child, choosing to live with the settled community with his two sons, Ossie and Tito. The horse forms an instant attachment to Ossie and moves into their Ballymun flat. When the neighbours complain, the horse is removed by the police who then illegally sell it on to a racehorse-owner.
Ossie and Tito steal the horse back setting off across the country to avoid recapture, pursued both by the police and by their father, who enlists the help of his old allies in the Traveller community to track down the boys. The chase goes through the midlands before the boys and the horse are cornered by the police on the edge of the Atlantic Ocean.