The winners are taken to the Tripod city in a pressurised dome astride a river. Inside the city, the boys encounter 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. The "gold" in the title refers to the city's color, while the "lead" refers to the heightened gravity.