The Next Best Book Club discussion

What is the best mystery (single novel, not series) you have ever read?

I liked And Then There Were None (10 Little Indians)
by Agatha Christie

The Day After Tomorrow
Do not read the ending first!! If you do you may as well not read the book. I felt like someone had punched me in the chest at the end. I made my husband read it, he made his sister read it, she made her husband read it and it went on and on.

I am a fan of both The Alienist and Murder on the Orient Express.

Off the top of my head I really liked Umberto Eco's The Name of the Rose including Postscript to the Name of the Rose.

Never really thought of it as a mystery until now, but I'll second El on Name of the Rose.