The City Of Gold And Lead by John Christopher

In this science fiction novel, three boys embark on a daring mission to infiltrate the alien Tripods' city, where they hope to uncover the secrets of their oppressors and find a way to free humanity. As they navigate the city's oppressive environment, they face numerous challenges and dangers, including the constant threat of discovery by the Tripods and the psychological toll of living under their control. The story explores themes of courage, resistance, and the struggle for freedom as the boys work to gather crucial information that could help humanity fight back against their alien overlords.