They Came to Baghdad by Agatha Christie
I actually finished this book last weekend, but I've been having a bit of a week and just forgot to post it here. This is a strange one for AC, although after WWII she did start to change things up a bit from the country house murder mystery plot. They Came to Baghdad was published in 1951 and is a Cold War era espionage thriller set in the Middle East rather than a the-butler-did-it English drawing room mystery.
