The title of the book kind of gives it away, but I hadn't read enough stories about androids at this point for them to be a trope and I like the series so much I don't think I even remembered the title, I just saw the spider and opened the book.
I think the part that sticks with me right off the bat was when they see Erek running and he hits a bus and then turns into a metal skeleton thing for a second and then turns back into Erek.
That sort of blew my mind, I was so confused as to what happened and just wanted to finish the rest of the book.
Oh dang this is the first we hear about the howlers.
And then of course that brutal ending scene where
spoiler
Erek destroys all of the controllers and saves all of the horribly dying animorphs
