Hey writers, what novel did you read that instantly became your favourite - and why?

Maybe I’m asking because I want recommendations, but I guess what I really want is to see if there are any commonalities across a sea of novels - regardless of genre or style. I’ll go first:

I’ve always loved ‘The Maze Runner’. It’s mainly because I’m a sucker for unexplained backstories with characters and circumstances. The first book kept me guessing the entire time. That’s probably why I also loved ‘The Fever Code’ (which is the book’s prequel).