I read two books about 30 years ago from a trilogy.I dont remember the name of the story or the arthur.It may have been written in the late 60s or early 70s.I never got to read the third book. Aliens had taken over the earth in the story. All the big cities were in ruin and the humans live in small farming communities.The Aliens had built their own cities where selected humans served them. When a young human became a certain age, the aliens attached a metal cap to their head so that they could be controlled.When it was time for the main character to have his cap attached,he and another boy ran away. They made their way to an old ruined city where they met up with another boy(Hes the only character whos name I can remember) His name was Jean Paul, but he was so tall and skinny that they called him Bean Pole. While in the city subway hiding from aliens that were hunting runaways they found some old weapons.They found some grenades, and figured how to use them.While leaving the city an alien patrol tried to capture them, and they used the grenades to destroy the alien ship.Later thay joined the undrground where they had fake caps attached to their heads.They then won a contest to be selectes as servents to the aliens in their cities so that they could spy on them.The main characters alien treated him like a pet and let him get close to him.He ended up killing the alien and escaping.I dont know what happened after that because I didnt get to read the third book.I have been searching for the name of this for 20 years.If any one can tell me the name of these books or the arthur,I would really appreciate it.