The Words the Walls Hear

We begin with an unwilling protagonist, two brothers working undercover and the killings of the ‘advanced’ humans but by the end we are left with the broken protagonist who has disappeared, a revenge seeking brother, the misunderstood suspect and a whole load more crap than a serial killer. So what happened? And what are these so-called advanced humans?  ***DISCLAIMER: Image does not belong to me. I have no right to the image therefore, all credits should go to the rightful owner!****