Complex sentence: Henry and Underhill make their way to Duddits, as Henry believes he is the only hope to defeat Mr. Grey; they find Duddits already packed up and ready to go as he knew they were coming.
Split into simpler sentences: Henry and Underhill make their way to Duddits as Henry believes he is the hope to defeating Mr. Grey. They find Duddits already packed up and ready to go as he knew they were coming.