Looking for a Thought-Provoking, Dark Mystery with Twists!

I’m searching for a book that will leave me thinking hard long after I’ve finished it. I’d love a gripping mystery, preferably a murder mystery, with plenty of plot twists to keep me guessing. Bonus points if it includes elements of romance and can delve into very dark or unsettling themes. A story that’s layered, unpredictable, and emotionally intense would be perfect! Any recommendations?