* CompleteMonster: [[EvilFormerFriend Neil Cassidy]], an obsessive, charismatic neuroscientist playing God with the minds of others, willingly [[EmotionSuppression destroyed his own personhood]] to better demonstrate the fundamentals of the Argument, a complex, nihilistic philosophy ruling everything as a mental construct. After graduating from college by the side of his best friend [[TheProtagonist Thomas Bible]], Neil was covertly enrolled in the UsefulNotes/{{NSA}}, where he performed immoral mental experiments on prisoners before going rogue to utilize that knowledge on civilians. Neil demonstrates a sick "love" for Thomas and conducts a horrific mind game with him at the center to realign his thinking back to the Argument. Along the way, Neil uses his power over people's brains to have a porn star cut herself to death with broken glass after rewiring her brain to masochistic tendencies; has a business magnate cannibalize a young girl and forces him to enjoy the experience; steals billionaire Theodoros Gyges's ability to recognize faces and drives him insane, resulting—and this might have been deliberate on Neil's part—in Gyges becoming a SerialKiller, known as the Chiropractor, who [[CruelAndUnusualDeath ripped out his victim's spines]]; and torments a televangelist with alternating sensations of divine relief and hellish damnation. This culminates in Neil murdering Thomas's--and possibly his own--four-year-old son Frankie and subjecting both Thomas and his ex-wife Nora to horrific mental and emotional torture that ultimately leaves Thomas broken as a person, all to demonstrate his twisted obsession with both Thomas and his long-abandoned philosophies. Suave, cool-headed, and utterly remorseless, Neil Cassidy took MindRape to an art form and left a trail of destroyed lives in his wake.
* FauxSymbolism: Thomas ''Bible''? His unusual surname is {{Lampshaded}} but it's not clear if it's meant to signify anything.
* MagnificentBastard: Neil Cassidy is a bastard, but he's charismatic, charming, and absolutely in control in every situation he's in. It turns out he's more or less made himself this way; [[spoiler: as a result of rewiring his own mind]], Neil's incapable of any empathy or even surprise and he's a perfect example of TheUnfettered, flawlessly executing his twisted mind game against Thomas with virtually no blunders on his part.
* NightmareFuel: Sprinkled throughout the whole book, but especially toward the end.