My Sister The Serial Killer by Oyinkan Braithwaite

The reader might suspect that this would be the case, but when you help your sister to plot a crime, one that you feel compelled to do, and it is to protect her from a very bad man, you make a life changing decision.  The book goes through the history of that initial crime, and then intersperses crimes that occurred subsequently, and then right up in to the present.
I love the way the story is written.  It really flows in a beautiful way, with both sympathy for the lead character, Korede, and a sense of foreboding about what her sister Ayoola will get her involved with.  It takes place in Lagos, and Korede is a nurse who is very well respected and her sister is the much prettier one of the two.  Ayoola is uses to getting her way and she is used to taking none of the blame for her actions.  Korede is used to literally cleaning up her mess.
It is a short novel, almost a novella, but one that you will be thinking about long after you close the cover.