For a quiet, literary approach that burrows into your subconscious, try 'Drive Your Plow Over the Bones of the Dead' by Olga Tokarczuk. It’s a murder mystery narrated by an elderly woman who is deeply eccentric, possibly unstable, and fiercely devoted to animal rights. The psychological tension comes from being trapped in her unique, sometimes paranoid, worldview. You’re never quite sure if her insights are genius or delusion, and that unreliable narration creates a constant, low-grade terror about what’s real and what’s justified. The horror is in the moral ambiguity and the unsettling charisma of the narrator herself.