When I was in high school, I devoured Agatha Christie books. My favorite was And Then There Were None - it's such a classic (and classy) British mystery.
P.D. James reminds me of a slightly - I say slightly, because the lady turned 90 this year - more modern Agatha Christie. There aren't any huge thrills in this story, and the culprit was fairly easy to figure out, but it was satisfying. I'll be reading some more James soon.