Finishing up with my Hammett...This one never held much attraction for me because I supposed it was going to parody the Agatha Christie type murder mystery and I prefer my Hammett straight up. 
 It was actually very enjoyable tho the mystery is not too difficult to figure out and, once you've deduced the "twist", it's pretty simple to decide whodunit. 
 Not sure why this was his bestseller. I'm an Op man myself.