The pool of fire

This is the conclusion of the Tripods series written under the name John Christopher. These young adult science fiction stories are set on Earth ruled by the alien Tripods. A prequel detailing the conquest was added 20 years later.

The series:

0.5 (Prequel) When the Tripods Came (1988)

1. The White Mountains (1967)

2. The City of Gold and Lead (1967)

3. The Pool of Fire (1968)