Complex sentence: The story is a sentimental romantic tale of a young Irish woman, Kathleen Clare, whose romantic ties to Kenneth Wayne are threatened by her adopted father John Carteret's memory of his thwarted love for her aunt, Moonyean Clare.
Split into simpler sentences: The story is a sentimental romantic tale of a young Irish woman, Kathleen Clare. Her romantic attachment to Kenneth Wayne is opposed by her adopted father John Carteret, who bears the painful memory of his thwarted love for her aunt, Moonyean Clare.