How to understand a second order Karma?

If a person **B** does an intentional harmful action on person **A**, and so **B** does a bad karma. As a result of that karma, it happens that a person **C** ends up hurting person **B**, intentionally or unintentionally. So what is the result of the action of person **C**? Does her action account for Karma? Does she even have any choice to hurt B or not hurt B? If **C** hurts **B** intentionally does that account for bad karma, but **C** did in because she had to as it was **B**'s karma? If this continues, this whole sequence will never ever end.