The Tripods

The Tripods is a series of young adult science fiction novels by Samuel Youd, written under the pen name John Christopher. The series takes place on an alternate Earth in which humans are enslaved by "Tripods" - large three-legged walking machines piloted by unseen aliens called the "Masters." The first three books follow an unenslaved young English boy who joins a resistance group to fight against and overthrow the Tripods' rule. The prequel, however, follows another English boy who witnesses the arrival of the very first Tripods.

Books

1. The White Mountains
2. The City of Gold and Lead
3. The Pool of Fire
4. When the Tripods Came (prequel)