I just finished The Tripod trilogy. Which is a bit misleading because John Christopher wrote 4 books so technically it isn't a trilogy. He wrote one, two and three then went back and wrote a prequel. I think you could start with the prequel and it would still all make sense, sometimes the prequel is like a sequel but just out of order but he did a good job with this one.
The books are basically about an alien invasion and brainwashing of all mankind by gigantic machine like things with 3 legs. Some people escape and form a resistance group. They are the only humans other then children under the age of 14 thatare free to think for themselves. The main character in the books is Will. He is a young boy that doesn't want to be like everyone else under the aliens powers. He finds the resistance group after a long adventure to their hiding place. He is joined by his cousin and another kid on the way and they become good friends thoughout the series.
The titles of the books in this series are: The White Mountains #1, The City of Gold and Lead #2, The Pool of Fire #3 and the prequel When the Tripods Came #4.
The Second book in the series was the best. The City of Gold and Lead. I liked it because it actually took you into the place where the aliens live. It was very creative and interesting to read about how they interacted with humans and what they ate. The part that stuck in my mind the most was how they thought some humans were beautiful and they killed them and put them in a glass case on display in a museum. They had them cataloged and labeled just like we might have a collection of butterflies. The aliens live so much longer then a human would so they probably thought that since there are so many of us and we don't live long anyway they could preserve the history of humans to look at long after our race is wiped out. Just like we think about butterflies. They also wanted to make a zoo where they kept people in their natural environment with air and water. Then the tripod aliens could come and look at them for years after the rest of the humans on the earth were long gone or extinct.
The last book, #3 is kind of depressing. Humans get rid of the aliens(tripods) and then start fighting again. One of the advantages of the aliens being here was no more wars between countries, everyone was united in worshipping the tripods. When they were gone we all went back to our differences and fighting. Sure this is agency working but it sure would be nice to just get along without aliens taking over the world and justifying it as being helpful to mankind.
The books were short and sweet. I would almost say they were WHOLE but I will go with HEALING. Oh I can't make up my mind, what do you think?