A Business Proposal

After all that the Winchester's have done for Castiel, he feels like he has never done anything for them. He feels that he has only made mistakes. In an attempt to do something for Sam and Dean he decides to save Adam from the cage. While working with Crowley, a spell to bring Adam into a highly warded cell backfires, trapping the angel and the king of hell inside. What events will unfold? How long will this "dynamic duo" remain trapped? Only god... *ahem*.... only Chuck knows.