Sister - by Rosamund Lupton

"Sister" is one of those books that you've never heard about, may never have picked up to read, but are extremely glad you did.  Beatrice is the "older sister" who lives in New York (having moved there from England), and who constantly "takes care of" her younger, artist sister who still lives in London.  Beatrice receives a phone call that her sister is missing - and returns to London to find her.  She eventually finds her - dead in a restroom at a park.  While her sister's death is ruled a suicide, Beatrice doesn't believe it, and sets out to figure out why her sister was killed, and who did it.

Thus, while at bottom the story is a murder investigation - the premise is interesting.  The story is told as if Beatrice is writing a letter to her dead sister.  Much of the story is Beatrice recounting a conversation she's having with the prosecutor in the case, after she's solved the mystery and has become their star witness.  As it's a letter to her sister, there are many parts that detail the relationship between the two sisters, as Beatrice realizes how much she didn't know about her sister - and how much she did know. 

Not many books have parts that make me actually cry.  While no tears ever escaped my eyes (I'm too manly for that - I'll admit), there was one moment, while reading on the recumbent bike at the YMCA, where I was glad my face was sweaty so if a tear did escape it wouldn't make me look less manly to the other folks lifting weights around me.  It was that good.  I heartily recommend this one to anyone.  You don't have to like detective/mystery novels to like this one.  It was good enough that I've already got her second book on hold at the library.