Nick Cutter's 'The Deep' is quite possibly the most disturbing book I've ever read.
It's not the scariest--I think that for a story to be truly terrifying you have to be able to, on some level, imagine it happening to you. That's why most of them start so simply--everyone can imagine going up to a cabin for the weekend, everyone can imagine taking a wrong turn late at night, everyone can imagine stopping at the wrong hotel. I don't think many people can imagine traveling eight miles straight down to an undersea base at the bottom of the Pacific Ocean in order to assist their brilliant-but-remote scientist brother in his efforts to harvest a miracle cure for a new disease using a substance unknown to science. It's not, y'know...common.
But 'The Deep' isn't scary. (Well, okay, it is actually pretty scary, but it's not primarily scary. If you get my meaning.) 'The Deep' is disturbing. 'The Deep' presents a vision of a universe that is fundamentally at odds with rationality--not simply a scary thing down at the bottom of the ocean, but a rot at the heart of everything we think we know about the way that reality works. The book isn't about insanity; it's almost the opposite of insanity, the attempts by fundamentally rational people to comprehend something that cannot be understood through rational means. I've read plenty of books where the big twist is that the main character is insane, but I don't think I've ever read a book before where I was hoping that to be the case.
'The Deep' has a magnificent purity to its commitment to sheer, sickening irrationality. None of it makes sense. The disease the characters are attempting to cure, a progressive memory disorder called "the 'Gets", has no apparent mechanism for transmission. It appears out of nowhere. The substance that apparently cures it, ambrosia, is sickeningly physics-defying and does things to people and animals that makes the Colour out of Space look like Turf Builder. Even the environment the story takes place in has a tendency to warp and shift in impossible ways, resulting in some of the most memorable and nightmarish imagery I've seen in a horror novel. It's almost like living a fever dream.
Even worse, it never feels like this is an ordinary world that is being corrupted. Several characters including the protagonist, Luke, have flashbacks to horrific events from their past that take on a distinct tinge of madness and impossibility. It feels almost as though whatever they've come in contact has been waiting for them all their lives, and I hope I'm not spoiling things too much when I say that this isn't too far from the truth. That rot is everywhere in 'The Deep' once you start looking for it. It stretches deep into the past and all the way down to the bottom of the ocean. It transforms the things it touches, and it has a purpose.
I cannot stress enough how much this book impresses me. It sets out to achieve a certain tone, a sense of creeping, inchoate, inexplicable chaos and it hits the notes so perfectly that I can't imagine any way of improving it. The novel never gives in to the urge to define its monsters in terms of myth or legend the way so many horror stories eventually do; it comes close, near the end, when you come face to face with the heart of the madness and find a little kinship to the monsters we all imagine to be trapped down below, but it never does anything as slapdash or lazy as saying, "Hey, it was Satan/C'thulhu/Killer BOB all along!" The book remains resolute in its commitment to utter madness on a cosmic scale, even as the ending makes perfect, inevitable sense. (That ending, man. That's going to haunt you.)
Cutter also manages to shed most of the trappings of Stephen King here. There's still a tiny amount--like King, much of the book centers on the father/son dynamic that King explored in novels like 'The Shining' and 'Cell'--but I feel like this book is where Cutter comes into his own. I don't think I'll wait long to pick up his next book.
Thank God that it doesn't sound as creepy as this one.