The series takes place in a post-apocalyptic world where humanity is enslaved by "Tripods" – gigantic three-legged walking machines piloted by an alien race later identified as the "Masters".
Human society is largely pastoral, with few habitations larger than villages, and what little industry exists is conducted under the watchful presence of the Tripods.
Protagonist Will Parker, a thirteen-year-old boy living in the fictional English village of Wherton, is looking forward to being Capped at the next Capping Day, until a chance meeting with a mysterious fake-Capped man named Ozymandias (taking his name from a poem he frequently recites) prompts him to discover a world beyond the Tripods' control.
Together with his cousin Henry and later a French teenager named Jean-Paul Deliet, nicknamed "Beanpole", they move off towards the White Mountains to avoid being Capped.
The novel climaxes with Henry and Beanpole discovering that earlier, when Will was captured by a Tripod, he was unknowingly implanted with a tracking device.
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 (hence the selection through athletic contests).
Will and Fritz (who had managed to escape the city after all) travel to Eastern Europe, the Caucasus, and the Middle East to organize resistance against the Tripods.
The resistance, having ambushed a Tripod and captured a Master, accidentally discover that alcohol has a strong soporific effect on them, and use this knowledge to simultaneously attack their cities.
In contrast to Julius' efforts to unite the world, the alliance built during the resistance falls apart, with nationalistic hostilities appearing and each country going their separate ways.
When they find it is also controlled by the Capped, they hijack a plane to Switzerland, which has managed to restrict its hypnotized population better than other European nations.
When the Swiss are eventually invaded and enslaved, the narrator and his family establish the "White Mountains" resistance movement of the original trilogy.
Editions have been published by: The series has been translated into Arabic, Dutch, Danish, Finnish, French, German, Hebrew, Persian, Spanish, Greek, and Mandarin Chinese (Taiwan).
To avoid an overuse of the mechanical Tripods, the producers invented a new faction, the "Black Guards," as a human police force with the task to enforce the will of the Masters.
On 4 January 2005, Gregor Johnson was hired to direct a feature film adaptation of The Tripods and rewrite the screenplay for Don Murphy & Touchstone Pictures.
[5] In 2009, Alex Proyas was hired to direct a feature film adaptation of The Tripods and Stuart Hazeldine would write the screenplay starting with "The White Mountain.