Complex sentence: The play was a partial adaptation by the author of his own novel "Sonata otoño", which had appeared five years earlier, and is about the adventures of the womanizer Marquis of Bradomin, an aristocrat with political sympathies for the "Carlistas".
Split into simpler sentences: The play was a partial adaptation of his novel "Sonata otoño", which had appeared five years earlier. This novel is about the adventures of the womanizer Marquis of Bradomin, an aristocrat with political sympathies for the "Carlistas".