Supernatural - and lo! they do it again

Ah, I have to hand it to SPN. Yet again I had all but stopped watching, and then I caught the last ep (ep 19 of S6 I believe) and lo! here I am and I've just inhaled eps 16-19 in one sitting.

Once more, at the last hour, SPN has swum up into my interest. Those of you who have been watching from the beginning may need to give me a refresher on what I've missed.

( A tale of hunters, angels and demons - SPOILERS up to and including ep 19, season 6... )