Complex sentence: The Sixth Doctor arrived on the 14th planet to collect Mentos by an alien cylinder that was holding Generios One, the capital planet of the system hostage, threatening to destroy it unless the people of Generios handed over their three greatest treasures.
Split into simpler sentences: The Sixth Doctor arrived on the 14th planet to collect Mentos. An alien cylinder was holding Generios One, the capital planet of the system hostage, threatening to destroy it unless the people of Generios handed over their three greatest treasures.