Castiel's grace was slowly losing its strength and with every passing day the deathly weight inside was becoming heavier, weighing him down. Was the end inevitable? He had always thought that he would serve God for eternity, being the faithful servant by God's side but since the apocalypse things had changed and now he wasn't so sure.
Angels had always had their secrets and they had always kept them but there was one secret that few humans and extra-terrestrials knew about and that, was that when an angel lost a stolen grace they didn't die. Not completely anyway, instead they turned to stone. In this form they were known as Weeping Angels and there was one way out of that form. As Weeping Angels they were able to use humans and send them back in time- this was done by making skin contact with them, although they could only move when the human was not looking- With every human they sent back they would gain a little bit of their grace and eventually their angelhood. But they always knew they had little time.
There was a man, named the Doctor and in ways he was not only a man but an alien in human terms and this man knew about the Weeping Angels and he knew their secret. The Doctor had not always known both sides of their secret but he had known of them and in ways the Doctor sympathised with them. To be stuck between lives with only one way out was hard and to be unable to communicate with others of your kind was harder and the Doctor knew this feeling well. But he also knew that the Angels were harming human kind and this was everything the Doctor stood against and they had to be stopped and if the Doctor knew of anyone that could help in this situation. It was the Winchesters or Winchester.
Little did Dean know, he was about to go on a road trip on a much larger scale than he was used to, to save both his brother and his best friend.
Now it was just a matter of finding Sam.