The Wild Irish Girl: Lady Sydney Morgan

When Horatio, the son of an English lord, is exiled to his father's Irish estate as a penalty for his corrupt ways during his life in London, he goes off in pursuit of adventure. In Ireland, Horatio finds a worn castle and the remnants of the Catholic Gaelic aristocracy that his predecessors displaced after the Cromwellian conquest of Ireland. Horatio learns about the past, culture, and language of a country he had once ignored. Still, he must remain in disguise because his English ancestors are responsible for destroying the Gaelic family he now loves. The story unfolds through letters written by Horatio to his friends.
It is a passionately nationalistic book and one of the first works discussing Irish nationalism. It represents the Irish condition initially from an English standpoint. With its incredible writing, gripping plot, and excellently portrayed characters, the novel immediately became a hit in England.