Madame Christie! i bow to you. :D

She is phenomenal at the "I know who it is! ...oh, apparently I don't" reveals. I wish more people managed that.

This was reportedly one of Christie's own favorites -- she reread it years later and noted in her diary that she thought it had stood up to time passing remarkably well.

I believe I recall really liking this one - it's been a while since I've read it.