Huh. I hadn't even considered the possibility of winning and thus, having to come up with a riddle. Ah well. I've posted this before, but it was a long, long time ago... so no using the search function to cheat, 'kay?
My treachery leads to your great deeds,
I've broken your family, then protected you from harm.
Because of me you safely escaped, because of me you had to.
My protection lasts only tonight.
Who am I, and who am I talking to? Extra kudos if you can tell me when. (It is LotR related)