The Mystery, Crime, and Thriller Group discussion

Just finished Shutter Island and LOVED it. Elements I liked:

-mystery of what was really happening to the psychiatric patients on the island (throughout most of the book) - mystery is my favorite story element;

-the surprise twist at the end (I refrain from reading reviews of books before I read them because even knowing that there is a surprise ending spoils it for me because I am constantly wondering throughout the book what the twist might be - but LOVE it when I don't know it's coming and am truly surprised);

-background setting/theme of insane asylums, mental illness

Any recommendations for books like this??

If you're all about twisty, you might want to try The Murder of Roger Ackroyd, by Agatha Christie. No mental illness, but definitely a hell of a twist .