Several random people are being snatched away with supposedly nothing that connects them; Sam and Dean suspect that demons are involved and investigate the case. While this is happening, Dean still feels guilty about Castiel not escaping from Purgatory with him (as seen in flashbacks)...until Cas randomly shows up with no memory of how he escaped.
Many fans rejoiced because of Castiel's appearance, it's great to see him back to normal and fighting alongside the Winchesters again. The question is quickly brought up by Dean: How did he escape? To my surprise, the question was answered in this episode rather than leave it hanging, but I will not spoil the surprise for you. However, the answer to the question did also bring up some new questions which will, I suspect, be answered in later episodes.
Not only did Cas make a big reappearance, we also see Crowley in this episode. It has been a few episodes since we last saw him, and he has been the main villain of this season, or at least is the one who stands in our protagonists way the most. Something I particularly loved about this episode was Crowley's character. In previous seasons Crowley has helped out the Winchesters (when it benefits him) and has become a likable character that makes jokes and witty comments, this episode really showed the dark side of his character that we don't always see. Yes, in the past we've seen Crowley torture and kill others, but generally it was to people who we didn't know well or care that much about (minor characters). Then we have this episode where Crowley is fighting against the good guys that we know and (arguably) care about. As much as I enjoy witty Crowley, I think having him as a cruel villain was a good reminder to the audience that he is in fact the "king of hell".
A very enjoyable episode! The past several episodes have felt episodic, or rather weren't really part of the main storyline (that doesn't make them bad at all, but at the same time it doesn't seem to really push the story along), but this one did have some interesting developments and I am looking forward to seeing what happens from them. I would give this episode a solid 8 / 10.