I am going on memory here because I haven't read this book in a while.
Before this book, Marco is just seen as a plain class clown with reservations about getting into this war because of his dad and his 'mother's death'. This book is important because it further introduced the character.
We see that yeah, Marco is capable of risking solo heroic action for the sake of saving an innocent. Yeah, he shows early hints of the 'calculating-strategist' in him. Yeah, he turns into a lobster. And yeah, by the time it ends, he is completely engulfed in this war the whole way because of his mum being the host of a powerful enemy.
I don't think he could have walked out of this one. He wouldn't know. But it wouldn't change the fact that his mother was still a Controller. That she is the force pushing for a peaceful-subtle style invasion and all.
Having said that, I think the coincidence of Eva being the host of none other than Visser One was a bit much at first. Why does there ALWAYS have to be the whole discovery of a relative or friend on the wrong-side behind every conflict fiction?? Who knows??
Once you see it as a plot device for the character Marco, it works really good though. It's adds an emotional challenge and further engages us with him.
I particularly liked the mental picture of them in their animal morphs and the sole gorilla dropping at the sight of her. The gorilla's mind being to close to a human's emotionally for Marco to mask his shock and sadness in. It was Jake that got Marco back together. KA wrote this to perfection.
The Visser rivalry adds a new depth to our early concepts of the hierarchy behind the Yeerk Empire.
Visser One saw Visser Three as ruining all her plans on the Invasion Campaign of Earth she had masterfully started. Always leaning towards subtlety, devised the sabotage as a means to get rid of him. This highlights them as the political leaders that they are, not just Yeerk generals.
There's also a bit more on adding some fun to the thus-far serious Ax in this book. I believe this is where he first goes beserk with the taste buds of the human morph. Classic, Ax.
Another part that I have not forgotten in the story in this book, that is touched upon at various points throughout the rest of the series, is the fight inside the ant tunnels. The Animorphs had their major fight for life, and it was against one of 'Mother Earth's' own. In many ways, worse than any other of their battles against the Yeerks. All taken place right out the back of an enemy's house. Things could have gotten seriously messy there.
A great book. One of my Marco's favorite.
oh right. I just copied the title. I forgot to edit that.
PS: Please also take note of your spelling. It's THE PR
EDATOR.