After his wife`s death, an alcoholic father, who once lived a gypsylike existence as part of a people known as the travellers, retires with his two sons to a dreary Dublin tenement. But the atmosphere brightens considerably when the children`s grandfather, who remains a traveller and does not approve of their city life, brings them a white stallion named Tir na nOg whom he has found near the Irish Sea. For a while, they all live happily in the flat, but when annoyed neighbors complain about the presence of a horse in an apartment building, police intervene and take Tir na nOg away. When an unethical cop illegally sells the stallion to a breeder who plans to train him as a racehorse, the boys, desperate to get him back, come to the animal`s rescue and free him. Tir na nOg then leads the children on an adventure through the Irish countryside, as their father, helped by some friends, tries to track them down. When the family is finally reunited, a magical event occurs that makes them realize the mystical powers that the animal possesses.