***Alert: Mild Spoilers***
This prequel to The Maze Runner trilogy has a prologue and epilogue that refer to characters from the other books, but have nothing whatsoever to do with the main story of this book. It's just weird.
This is the story of how The Flare began - a virus released as a population control measure after apocalyptic sun flares killed billions of people, but apparently there's still not enough resources left on earth for the people who are left. The story follows Mark (a wimpy teenager who only has any strength when he's filled with rage - but at least he's not a stereotype) and the group of friends (but mostly just an old ex-soldier) he survived the apocalypse with as they try to figure out who released the mutating virus and why. They run across a little girl who seems to be immune, and realize their one final act (since they're infected), should be to deliver her into the hands of the people who released the virus and hope they can use her to make a cure. If you've read the trilogy, you'll know that didn't happen, so all the struggles Mark and his friends went through were pointless.
That's not the only thing that takes away from the attempt at tragic heroism in this book, however. It's also the endless string of impossible fight sequences (how many times can two people fight off hoards of savage lunatics without sustaining severe, immobilizing injuries? Plenty, apparently.) It got to feel like repetitive filler.
This book lacked the character and relationship development of the original trilogy - it was almost all action. I found Mark's "flashback dreams" to the sun flare catastrophe to be the most interesting part of this book, and I almost wish Dashner would've made that the focus of this book. It's a much more interesting story. We don't get much of a satisfying conclusion - Deedee walks through the Flat-trans and we are left with unanswered questions. The Kill Order was just not as inspired or inspiring as the other books in the Maze Runner series.