I actually waited a few days before writing this review on purpose. Usually, I get them out late because I'm busy, but in the case of this one, I actually waited until I had cooled down, and felt I could talk about it rationally, rather than just flailing and yelling and crying and virtually punching things. Now that I'm in a better frame of mind, let's talk about Supernatural's mid-season finale.
First, the plot. A lot was going on here. Maybe too much, actually, but I'll get to that in a second.
So, the main plot centers around a civil war between the different factions of angels at war on earth. On one side, you've got Bartholomew, and on the other Malachi. Each of these angels are leading a group intent on taking over Heaven. Each side is slaughtering the other, and Sam and Dean pick up a lead. When they get there to investigate, they find Cas already on the case. Ezekiel, unhappy about being around so many angels, and especially Cas, forces Dean to send Cas away, which of course breaks everyone's hearts.
So, Cas is a bit lost and confused and alone, so he tries to pray. Unfamiliar with the process from the human side, at first it doesn't seem to work, but he then receives a visit from Muriel, an angel who is attempting to stay out of everybody's fighting. She's scared to see him, because obviously Castiel could attract a lot of unwanted attention. Turns out, Muriel was right to be afraid - Malachi and some angel named Theo show up and kidnap Cas and Muriel. They attempt to force Cas to give up information about Metatron's spell. Cas is tortured, and Muriel is killed while they are trying to make him talk. Cas of course continually says all he can say - he didn't know what Metatron's plans are, and he's just as clueless as the rest of them as to how to get back into Heaven. When Malachi leaves the room, Theo reveals that he wants to defect from Malachi's side and join Metatron. Cas plays along for a moment, pretending he has pull with Metatron, and thus tricks Theo into letting him go. Cas steals Theo's grace and escapes.