Synopsis of 12×19: Castiel returns from his time in Heaven, first to kill Kelly and her unborn Nephilim and then to save them from being killed.
“The Future” opens with Kelly attempting to do everything in her power to defy Dagon. Dagon happily announces all of the evil plans they have for the child. Kelly looks at herself in a broken mirror and decides she can’t let him be born. As she apologizes to her son, she explains she can’t allow him to live if he was going to destroy the world. Kelly slits her wrists and the camera pans away slowly to emphasize the suicide attempt. However, this is Supernatural and death is rarely an option.
Sam and Dean are in the bunker attempting to figure out where Kelly is when Castiel returns from his sabbatical from Heaven. Dean angrily lectures Cas, mostly to hide the fact that he was worried. Castiel apologizes and explains he went back to Heaven to try to help. He feels like he has been nothing but a failure to Dean and Sam, and bluntly asks Dean whether or not they would be able to kill an innocent if that was the only choice. Dean dodges the question and says that they will find a better way. This conversation should have also happened four seasons ago, but better late than never.
Kelly isn’t dead because the Nephilim kept her alive, and Kelly is now a firm believer that her son is going save the human race. Sam and Dean figure out that they could use extracted grace to save both Kelly and the kid. They attempt to call Cas to deliver the good news, but then realize that Cas stole the Colt and was going to kill Dagon and Kelly.
Lucifer loses his mind with Dagon after Cas escapes with Kelly, and threatens to kill her if she is unable to find Kelly again. As Cas and Kelly drive, Cas explains that he is going to bring Kelly to Heaven, where both she and her son will die. They have a very existential conversation about whether or not the child is born inherently evil or good. Cas struggles with the answers to this and asks who will raise the child to hold these values after she dies. Kelly doesn’t have a response, but has a vision of Castiel protecting her child.
The Winchesters find Kelly and Cas, which leads to an argument that results in Dean sending them to the Impala. While Dean and Sam attempt to hash out what they are going to do, Kelly steals the Impala. Kelly decides that they are going to go to the sandbox.
Of course, Dagon meets them at the sandbox and kills the angel about to bring Kelly to Heaven. Dagon kills the angel, which causes Castiel to stand in front of Kelly to protect her. Castiel and Dagon fight, but Dagon easily overpowers him. The Winchesters rush into the fight, but Dagon beats the crap out of them and destroys the Colt. Cas tells Kelly to run, and she refuses, instead opting to hold his hand. The Nephilim transfers power to Castiel, turning his eyes yellow and making Castiel powerful. Cas kills Dagon and utters one of the lamest lines of the episode, “It is a miracle.”
Cas heals Dean and says he has faith that the child needs to be born with all of his power. Either the baby mind whammied Castiel, or the child does have the opportunity not to be evil. Regardless of the reason, Cas once again fails to see himself as a part of the Winchester team. Cas knocks Dean and Sam out proclaiming that the child showed him the future. Cas and Kelly drive off into the night, leaving the Winchesters unconscious in the park.