Complex sentence: On this floor Gwyneth appears, furious at Petunia and Primrose and their incompetence, and sees the darkling and manages to capture it, and takes the Creator, and knows it is from a dragon.
Split into simpler sentences: On this floor Gwyneth appears, she's still furious at Petunia and Primrose for their incompetence, sees the darkling then manages to capture it. She takes the Creator, and knows it is from a dragon.