I read these books when I was in late elementary school through 7th grade. I am posting all of them which I own. When I was younger I really enjoyed them.
The Yeerks have decided to try a little experiment. They've decided that if they can develop a way to make people more "willing" to be infested, they can speed up Earth's invasion. So, the Yeerks try to invent a substance that will take away the human ability to make a decision. A substance that will eliminate free will.
Now the Animorphs and Ax are not only faced with trying to slow down the Yeerks' invasion, but they also have to put an end to the genetic testing on a small group of humans. This time there's only one chance to stop the Yeerks. And if anything goes wrong, it's all over...
An okay story in the series, but the plot holes get annoying. When are they going to use a consistant bird morph that allows them to travel in groups and not worry about riding thermals? If Ax's race is so smart, why does he say and do the most naive things?
Though it is a fun series to read, there are times I wish I were a kid so I wouldn't notice this stuff.
My daughter loved it. She could not put it down.