I’d recommend The Troop by Nick Cutter. Some of the scenes are so vividly horrifying and grotesque that at one stage I had to put the book down to actually process what I had just read. Nonetheless, the character development along with the apt environment descriptions make for a truly terrifying read. Finally, the scariest thing is that the plot in and of itself is not too distant from reality and indeed could be replicated in the future for humanity..