First time any long term side character (who wasn't "in the know") learned about the Animorphs and the invasion. At one point when Marco was about to save his dad the text went into italics for a paragraph, emphasizing the significance of what he was about to do, making it that much more dramatic.
But you're an Animorph, my rational mind argued. A soldier. You have to let it happen. You can't save him now. Even temporary freedom would mean the end. The Yeerks won't stop till they find him. Find you. Your friends. You have to let it happen. It's the smart thing to do. The only thing to do.
That was it. This was the end of smart. And the beginning of right.
Nora became a Controller. Marco told his dad about the Yeerks and Visser One, staged his death and retreated into the mountains, then killed Visser One and saved Eva. Things went past the point of no return.
After so many books where it
seemed like someone would die or it
seemed like something big would change, finally one of the central villains was actually killed off and one of the series' major story arcs - Marco's struggle to save his mom - was concluded.
And in addition to all that, the book concludes with the Animorphs finally contacting the Andalite fleet.
The book had a
huge sense of momentum, especially after the long lack of story progression in the preceding books. First chapter, Marco's dad starts talking about zero-space, and the next chapter ends with him saying, "You know what? This Zero-space discovery? It's big. Really big. I don't think our lives will ever be the same."
During a highway chase Marco takes Exit 54, insinuating that the final book was approaching. And at the end of the book, Scholastic even slipped a cryptic message from the Yeerks into the text (We do know who they are... and we know you, too...) to screw with our young minds. I didn't know about the final arc back then - I didn't know that the books were ending until the countdown appeared on #51 - so #45 was an incredibly exhilarating change of pace. Plus, the Animorphs logo changed.
Pretty much all the earlier books that were very relevant to the overall arc were mostly introducing new elements that would become staples of the following books. But book 45, instead of introducing anything really new, took several big elements that were already in place and twisted them around and changed the dynamics of the story so that things couldn't be the same afterwards.
