Final answer:
The most frightening aspect of Christopher's journey to London is the sense of impending danger and uncertainty that he experiences throughout the journey.
Step-by-step explanation:
The most frightening aspect of Christopher's journey to London in the extended section of the novel is the sense of impending danger and uncertainty that he experiences throughout the journey. As Christopher navigates through the unfamiliar streets of London, he is constantly on edge, unsure of who he can trust and fearful of the unknown. This creates a tense and suspenseful atmosphere that keeps the reader engaged and invested in Christopher's story.