The first of the 'Megamorphs', a four book series that is integral to the narrative of the 'Animorphs', but the publishers decided to leave them out of the traditional numbering, possibly because of the length/price difference. This will forevermore confuse readers.
There's another four books, the 'Chronicles', that are similarly spaced out but they are mostly even longer and mostly set far before the Animorphs were given their powers. I chuck fan theories away and always go by publication order
'The Andalite's Gift' describes the group confronting a deadly new enemy and follows the perspective of all six Animorphs. It also gives a possible answer to my question of what happened to the woman the group saved in 'Invasion'? There's no direct link acknowledged, but Rachel finds a woman living alone in a shack of the woods. She is mentally broken and paranoid that the Yeerk will come back into her head. Good enough.
With such a dangerous menace hunting them down, the Animorphs get creative and there are some great plans executed. Best of all is continued information that the Prince Elgangor and Ax may not have given the Animorphs the whole picture regarding the Yeerks....
Next: 'The Alien'
Previous: 'The Stranger'