Christopher John. The City of Gold and Lead. Tripods 2

New York, London: Simon & Shuster for Young Readers, 2003.
The novel was first published in 1968.The Tripods is a series of young adult novels written by John Christopher, beginning in 1967. The first two were the basis of a science fiction TV series, produced in the United Kingdom in the 1980s.
After a year in the White Mountains, the resistance charges Will, Beanpole, and a German boy, Fritz, to infiltrate a Tripod city by competing in a regional sporting exhibition. Will, a boxer, and Fritz, a runner, win their respective contests, while Beanpole fails to win in the jumping events.
The winners are taken to the Tripod city in a pressurised dome astride a river. Inside the city, the boys discover the Tripods' operators, whom they refer to as the 'Masters'. Human males are slaves inside the cities, while beautiful females are killed and preserved for the Masters to admire. Slaves are furnished with breathing masks to survive the aliens' atmosphere, but are rapidly exhausted by the stronger artificial gravity and must therefore be periodically replaced. Although Fritz is abused by his Master, Will is treated as a pet by his. Eventually, Will's Master reveals a plan to replace the Earth's atmosphere with the Masters' toxic air to enable full control of the Earth. When the Master finds Will's diary, Will kills him to maintain the secret. With the assistance of Beanpole, Will escapes, and they return to the White Mountains. The story's title refers to the gold colour prevalent in the
Masters' cities, as well as the leaden weight of the increased gravity on the human slaves.