Megamorphs 1: The Andalite's Gift by K. A. Applegate

The Andalite's Gift is both a pause from the marathon of the main series, and a strange kind of relay race for the Animorphs. This book is about exhaustion both mental and physical, terror, more nightmares, and losing oneself, with a little bit of hope at the end.

It has a strange place in the continuity because it addresses some consequences from The Stranger, but it can't move the story forward because people might miss something important then. What it does do is give the first glimpse of Ax's perspective because of the rotation narration, and it lets us see what each Animorph thinks of each other in relation to the same event. Cassie does the first in what will be an ongoing thing of her carrying out amazing and almost impossible feats of morphing and it's really cool to read, but unfortunately the Megamorphs books are stuck within the continuity in a way that means they can't work as a sample of this world in the way that the various Chronicles books are able to in a pinch.