Josephine Tey, whose real name was Elizabeth Mackintosh, only wrote eight mysteries under her pseudonym, and judging from what I've read so far, they're all pretty much perfect. Not only that, but each is perfect in a different way. In To Love and Be Wise Inspector Alan Grant investigates the mysterious disappearance of an American photographer from an artist's community in the English countryside. What is particularly impressive about this book is that what makes it great is its resolution. It gets better as more gets revealed, which, if you read enough mysteries, is very very rare.
Some more book covers to enjoy: