With Sam's life on the knife-edge, Dean appeals to the fallen angels for help. Unfortunately, most of them only see Dean as a means to get to Castiel and exact vengeance on the one who caused them to Fall.
Dean and Sam take a captive Crowley to the Men of Letters base in the hopes that he will give up the names of the people possessed by his minion demons. But before they can get any information they are called away to investigate the disappearance of three soldiers.
Castiel makes his way to the Winchesters but discovers a band of angels are hunting him, intent on exacting vengeance for what they believe is his role in their fall from Heaven. Meanwhile, Ezekiel continues to repair Sam, but informs Dean that there is a price to be paid.
With the help from Charlie, Sam and Dean inadvertently release two individuals contained inside of the Men of Letters bunker who where both imprisoned in 1935. They soon discover that one of the individuals is Dorothy of Oz, and she is hot on the trail of the Wicked Witch of the West.
To track down a killer, Dean uses a spell which allows him to speak with the only witness, a German Sheppard. However, he soon discovers that everything is going to the dogs when the spell starts making him act like a canine as well.
Castiel is working as a convenience store clerk and learns of a series of local disappearances. He call the Winchesters, but Dean insists on Sam staying with Kevin to research the demon tablet while he help Cass.
Sonny, a man who runs a boy's home, calls Dean for help after a mysterious death. When Sam wonders how his brother knows Sonny, Dean explains that he spent two months at the boy's home when he was 16, after being arrested for theft.
When members of a virgin chastity group are abducted, Sheriff Jody Mills asks Sam and Dean for help. The Winchesters go undercover to track down the missing members, but when Dean disappears, Sam and Jody end up having to track him down.
The angels are embroiled in a bloody civil war, and Castiel is swept up in the conflict. Meanwhile, Dean realizes that Ezekiel is not who he claims to be and tries to warn Sam with dire results.
Dean and Castiel make a deal with Crowley in order to contact Sam's consciousness so he can expel the angel Gadreel from his body. However, Abaddon is hot on their trail and Crowley has plans of his own.
Crowley turns to Dean for help to locate the First Blade, the only weapon that can kill Abaddon. However, the trail leads them to the biblical Cain. Meanwhile, Sam asks Castiel for help when they need to extract the remaining angel grace from Sam's body to track Gadreel.
Six months after his disappearance, Garth turns up injured in a hospital. Sam and Dean arrive separately to investigate and soon discover that their friend has undergone a startling transformation.
Two dead victims show up with all the fat having being stolen from their bodies. Sam and Dean go undercover in order to investigate a local spa, and discover that a monster is preying on the overweight.
While Sam and Dean try to track down Kevin's mother, Castiel is captured by an old battle-comrade and learns more about the factions of angels.
The Winchester brothers investigate a murder that was apparently caused by a ghost. Sam and Dean discover that the Ghostfacers, Ed and Harry, are already on the case.
Sam and Dean are searching for the First Blade and end up having to track down the missing Crowley and discover that he's now thoroughly addicted to human blood. The Winchesters decide that going cold turkey is the only way.
When Dean chooses to stay in the bunker and try and locate Abaddon, Sam goes to a small Illinois town to investigate a string of vicious murders committed by seemingly harmless individuals.
Castiel investigates the mass slaughter of angels and finds a lone survivor and an old friend. Meanwhile, Sam and Dean capture Gadreel, and Metatron begins the ending of his story.
Sheriff Jody Mills befriends a young girl on the run from vampires. When she's forced to kill one of the monsters, Jody calls in Sam and Dean for help. However, they discover that everything isn't at it seems.
Sam and Dean learn about a monster killing in Chicago and head there to investigate. What they find is a young cop whose girlfriend was killed by the same creature, and who is caught between five powerful clans of monsters who jointly control the city.
Abaddon finally gets something that she can use as leverage against Crowley to force him to lure the Winchesters into a trap. Meanwhile, Castiel rallies his forces and asks Sam and Dean to come in and help him interrogate a captive angel with ties to Metatron.
After an angel carries out a suicide attack on an ice cream shop to kill one angel from another faction. Sam and Dean investigate and discover that the target was one of Metatron's angels and that Castiel may be responsible.
After attacking Gadreel, Dean leaves with Crowley to track down Metatron and kill him. Meanwhile, Gadreel takes Castiel into Heaven to try and break Metatron's connection to the angel tablet.