Provide a detailed summary of a fictional book titled "The Last Sentinel". The book is set in a futuristic world where the government has implemented extreme surveillance measures. The protagonist, Eira, is a young woman who discovers a way to bypass the surveillance and starts a rebellion. The summary should include at least 5 key plot points and highlight Eira's development throughout the story. Your response should contain at least 300 words and highlight at least 2 sections in your answer.

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