Dean is driving the Impala when Castiel appears next to him. He tells Dean that he's looking for Crowley and isn't sure how he's still alive. Dean makes it clear that killing Crowley is their first priority, but tells Castiel that they haven't found anything yet, either. Sam is tracking a Djinn in Omaha, and so Dean is going there to meet him. Before Castiel leaves, Dean asks him to call if he gets into real trouble.
After Castiel leaves Dean, he meets with Crowley, who is busy experimenting on Eve's body. Castiel reminds Crowley of their ultimate goal - opening the door to Purgatory - and Crowley gets angry. Eve could have opened the door to Purgatory, but Castiel let Dean and Sam kill her, and now he has to find another way in. He also accuses Castiel of being distracted because of the Winchesters - he can smell "the stench of the Impala" on him. Castiel tells Crowley that he had to check and see what they knew, and Crowley says that he knows they're after him and he's worried about Castiel's conflict of interest.Castiel admits to himself that he does have a conflict of interest. He still considers himself the Winchesters' guardian because of everything they taught him and everything they accomplished together. After the Apocalypse was averted and Castiel resurrected, he healed Dean, resurrected Bobby, and then went to Hell to resurrect Sam. He thought he'd managed to bring back all of Sam, but he realizes now that he was being arrogant, and that he should have known something was wrong with Sam. So, when Crowley tells Castiel to kill the Winchesters, he refuses. Crowley says that he'll kill them himself, but Castiel says he'll just bring them back and that Crowley shouldn't worry about them. Instead, Crowley needs to focus on finding Purgatory, or they will both "die again and again until the end of time."
Meanwhile, Sam and Bobby are interrogating a demon named Red about Crowley. Dean appears - he was lying when he told Castiel that Sam was in Omaha - and tells Sam that he wants to bring Castiel in the loop. Dean doesn't believe that Castiel is working with Crowley, but Bobby and Sam aren't so sure. As they discuss the possibility of a "Superman who's gone dark side" and the need for kryptonite, Castiel watches them, unseen. He's there when they torture the demon into revealing that he works for Crowley through a dispatcher named Ellsworth. Castiel is aware of Ellsworth, who he describes as the demon counterpart to Bobby, and because Castiel knows that they're getting close, he pre-emptively kills Ellsworth and the other demons at his headquarters.While Dean, Sam, and Bobby burst into Ellsworth's headquarters and find nothing, Castiel watches, and remembers Heaven after stopping the Apocalypse. The other angels, including Rachel, believed that God resurrected Castiel so that he could lead them, but Castiel told them that they had free will and didn't need a leader. They were lost without direction, however, and Raphael stepped in. He wanted Castiel to give him his allegiance and then help him to free Lucifer and Michael so they could restart the Apocalypse. When Castiel refused to join him, Raphael easily overpowered him.
Back in the present, Dean convinces Sam and Bobby to call Castiel, but Castiel doesn't appear when Sam prays, too afraid of the questions they'll have for him. Just as they turn to leave Ellsworth's headquarters, though, more demons appear. They are assassins sent by Crowley, and Castiel appears and quickly dispatches them. Dean, Sam, and Bobby take this to mean that Castiel is on their side, and they apologize to Castiel for doubting him. He forgives them for thinking he was "Superman going to the dark side" and agrees with Dean when Dean says they can "put away the kryptonite." He doesn't realize it at the time, but because of what he says, Dean realizes that Castiel has been spying on them.Castiel goes to confront Crowley, who he tells not to touch a hair on the heads of his friends. He then reveals the reason he partnered with Crowley: after Raphael beat him so easily, he considered going to Dean for help, but Crowley waylaid him and offered him a deal. Together, they would open Purgatory, and then they both would use the monster souls inside to grow more powerful. Castiel needed to be more powerful right away, however, so Crowley advanced him 50,000 souls, which Castiel used to overpower Raphael and then start his civil war in Heaven.
After threatening Crowley, Castiel answers another call from Dean, who is still at Ellsworth's headquarters with Sam and Bobby. Sam tells Castiel that they've figured out a way to track Crowley, and Castiel walks straight into their trap. He is surrounded by a ring of burning Holy Oil, and they start questioning him about Crowley. He tells them that he is working with Crowley only because he needs to defeat Raphael, and that they need to trust him. He then reveals that he is the one who resurrected Sam, and Sam asks Castiel if he purposefully raised him without his Soul. Castiel denies it, but it's clear that Dean, Sam, and Bobby no longer trust him. They tell Castiel that working with Crowley is wrong, and he knows it, which is why he kept his actions a secret from them. Castiel seems repentant, but when a cloud of demons appears outside, he tells them that it's too late to go back now. Dean, Sam, and Bobby flee the approaching demons, and Crowley soon appears to free Castiel from the burning holy oil.Castiel goes to visit Dean at Bobby's house. He tells Dean that he wants him to understand what he's doing and to know that he's doing it all because of what Dean taught him about free will. Dean tells Castiel that he's like a brother to him and that he needs to trust him when he tells him not to work with Crowley. If he keeps trying to open Purgatory, Dean will stop him. Castiel tells him that he can't stop him, apologizes, and then leaves.
Castiel is alone, praying to God. After having told his story, he asks again if he's doing the right thing. He begs for a sign and says that, if he doesn't get one, he's going to do whatever he must. There is no sign.Summary from Supernatural Wiki