This is the third and last of the "Tripod" trilogy, picking up almost exactly where "City of Gold and Lead" left off. Will has returned to the resistance base camp in the Swiss Alps. Enough information is passed on about the Masters (who ride in Tripods when outside of their city) and their cities to allow specific plans to be started to overthrow them. Will has found out that the Masters plan to kill all humans and replace earth's atmosphere with their atmosphere so they can begin living there. This plan is well on its way, and a ship from the Masters home planet should arrive within 3 or 4 years to begin this process. To learn more about the Masters physical capabilities, a Tripod is ambushed and a live Master is captured and put in a special area, like a guarded zoo area, based on information Will provided. It is discovered that a small bit of alcohol totally incapacitates the aliens, so a plan to put alcohol in the drinking water of the Tripod cities goes into action. Will and Fritz return to the city they were slaves in, and successfully stupefy all the Masters. They travel to the energy source of the city, the "pool of fire", and successfully open the outer doors allowing a crack to be made in the city covering. This kills all the Masters in that city. Two such other attempts in the other two Tripod city are made, one other city is successfully destroyed. But one city remains standing, and a new tactic has to be employed, that of dropping a bomb on the outer shell of the city by means of hot air balloons.Eventually all three cities are destroyed, and humans win their freedom and begin to set up a new government that will help them rediscover the lost ways of the ancient humans, before the Tripods ruled the earth.