Sam, Dean & Bobby go into the Campbell's secret library looking for something about the Mother of All. They stumble across a book that says the ashes of a Phoenix can hurt her. So then they start looking for information about a Phoenix. Dean stumbles across the journal of Samuel Colt and in it he says that he killed a Phoenix. So they have a time and place on where to get Phoenix ashes. Dean suggests they go back in time and call upon Castiel.
Castiel agrees to do it but he can only let them stay for 24 hours since anything longer than that will be hard to retrieve them. So Dean is excited because he loves the old west and he goes shopping. Once there they witness a hanging. The man getting hung threatens the people hanging him and then dies. But he's not really dead and comes back to kill those responsible for his death.
Sam goes to find Samuel Colt to get him to kill the Phoenix and Dean stays back to entrap the Phoenix, which is the guy that was hung. He gets one of the guys he's after and uses him as bait in the jail. The Phoenix comes but iron hurts him so he shoots the guy in the jail cell and chases after Dean.
Sam finds Colt and after convincing him that he is from the future by showing him his phone, he lets him take the Colt since he's retired. Sam comes back just in time while Dean is being chased and a showdown happens and Dean kills him. Just as he's about to gather the dust they get zapped back to the present.
Castiel gets wounded by his Lieutenant when she confronts him on the things he's doing to win the war. Which apparently are not good things. He kills her and then makes it back to Bobby's. He says he can't bring Sam and Dean back because he's still weak but if he can touch Bobby's soul he can regenerate faster. So that's what he does and it's not pleasant for Bobby.
All hope seems lost when the boys get back without the ash but there's a knock on the door. It's a package for Sam Winchester from Samuel Colt. It's the Phoenix ash and he apparently got the address from Sam's phone. So now they have something to hurt the Mother with.