Following the season 7 premiere, Castiel is taken over by the leviathans that he sucked out of Purgatory. This episode begins with a weakened Castiel-turned-leviathan leaving Dean and Bobby with a promise to deal with them later. He heads out into a lake and dissolves into black cloud of water that erupts out flowing in all directions … right into the local water supply, which allows the leviathans to begin taking over unsuspecting residents.
The vessel of Castiel appears to have not made it through the process, leading me to believe that Misha Collins (the actor who played Castiel) is gone from the show, at least for the foreseeable future. Dean certainly laments him, as he finds his trademark trenchcoat floating in the lake.
Sam is having some problems of his own, of course, as he’s having visions of Lucifer, who’s telling him that he never actually escaped from the cage where he trapped Lucifer and Michael (back at the end of season 5). Instead, Lucifer claims to have been inspiring this delusional post-apocalyptic “escape” as a way of torturing Sam. Dean claims that Lucifer isn’t real, but then that’s also what Lucifer says about Dean, so it’s hardly a compelling argument.
The leviathans begin taking over people in town, including a young girl. Some of them take over members of the swim team and then oon to devourr the rest of the swim team, but this doesn’t sit well with some of the others. In discussions among themselves, the leviathans mention “the boss” who seems to want them to stay under the radar. The little girl kills a surgeon and transforms into him. Having taken his place, the leviathan then kidnaps a woman from the hospital for a little midnight surgery.
Things get a little crazy as Sam and Dean go to help Bobby investigate a group of leviathans, but it turns out that Dean isn’t really there. Sam’s having another hallucination. (The odd thing here is that Dean was the one who drove them to the warehouse. If it were purely a hallucination, it’s not really clear who was driving the car. I suppose it’s possible that Sam was driving it and hallucinating that he wasn’t.)
Dean finally tracks down Sam, who’s in the middle of an argument with Lucifer. Not knowing who to believe, Sam pulls a gun on Dean. Dean’s able to convince him that the pain of this world – such as the physical pain from his injured hand – feels different from the pain of being tortured in some demonic hell. As Sam feels pain, Lucifer seems to fade away.
Dean: We got you out, Sammy. Believe in that. Believe me. You’ve gotta believe me. You’ve gotta make it stone number one and build on it. You understand?
With Sam sort of holding himself together, they get a call from Bobby letting them know that there are leviathans at the hospital. They head back to Bobby’s house to meet up with him, only to find that someone’s gotten their pyromania on. The building is a burnt out shell.
There’s no sign of Bobby at the house, fortunately. They do run into one of the leviathan-possessed people, though, who says that they’ve been found important enough to be targeted for execution. Sam’s able to escape when Dean causes a crane to drop a car on the leviathan.
The fight ends with Sam unconscious and Dean with a broken leg, so Dean has no option but to call for an ambulance. When Sam wakes up, he sees Lucifer again. Lucifer admits that he’s not real, but still says he isn’t going anywhere, which triggers a series of convulsions from Sam. Dean then learns that the hospital they’re heading to, Sioux Falls Hospital, is the one where Bobby found the leviathan.
The episode fades away with an image of Bobby’s junkyard, with the leviathan’s blood flowing back into him. Apparently, even having a car dropped on these guys only slows them down for a little while.