Chapter 1- Broken

Starting from season 4 episode 13 we see an AU where the story changes completely with an act of kindness from Caroline to Klaus. Caroline had set out to reconcile with Elena and instead is met by Klaus, who mourns the death of his youngest brother while trapped in Elena's living room by the Bennet witch Bonnie.
How will Caroline satiate Klaus' new found bloodlust for the doppelgänger? And what happens when an unknown figure from the Original's past comes into the picture?