The Black Hour, Lori Rader-Day

Just a stunning book I will never forget - the kind that subtly redefines the mystery/thriller genre the way Tana French's In the Woods did. I never knew what was coming next, and was frequently not just surprised, but shocked. 

Mostly what stays with me is the incredible level of psychological insight: at the level of the characters, Rader-Day captures the individual experience of depression and suicidal impulse, but she also really nails the elite grad school experience, which is both part 'country club in training' and has this underbelly of sex and violence (whether that's rape, or mugging, or school shooting, or just cut-throat ambition and cruelty).

It's not a 'fun' read, but it is gripping. Definitely looking to read more by Rader-Day soon.