While Sam hangs on the edge of life and death, Dean appeals to the fallen angels for help. Unfortunately, most of them only see Dean as a means to get to Castiel and exact bloody vengeance on the one who caused them to Fall. Meanwhile, Sam wrestles with his inner demons and Castiel learns what it means to be human.

Dean and Sam take a captive Crowley to the Men of Letters base in the hopes that he will give up the names and host bodies of his minion demons. However, they are called away to investigate the disappearance of three soldiers, which leads them to Abaddon, the Knight of Hell... and forces Ezekiel to take control of Sam's body to save his life.

With some help from Charlie, Sam and Dean inadvertently release two individuals contained inside of the Men of Letters bunker: an evil witch, and a young woman, both imprisoned since 1935. They soon discover that the woman is Dorothy of Oz, and she is hot on the trail of the Wicked Witch, who plans to summon her evil army to Earth and conquer the planet.

To track down a killer, Dean uses a spell to talk to a German Sheppard that was at both murders. 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 Tablet while he investigates.

Sonny, a man who runs a boy's home, calls Dean in after a mysterious death occurs. When Sam wonders how his brother knows Sonny, Dean explains that he spent two months there when he was 16 after being arrested for theft.

When a mysterious abductor targets members of a virgin chastity group, Sam and Dean go undercover to track down the killer when Sheriff Jody Mills asks them for help. However, Dean disappears and Sam and Jody end up tracking him down.

The angels fight each other in 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 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, they soon discover that the trail leads to Cain... the Father of Murder and the most powerful demon of all time. Meanwhile, Sam asks Castiel for help when they need to extract the remaining 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... and found others who share his condition.

Two victims die and the fat is stolen from their bodies. Dean and Sam investigate a local spa and go undercover, 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 brothers investigate a mysterious murder that was apparently caused by a ghost, and discovers that the Ghostfacers, Ed and Harry, are already on the case. However, the facts don't add up and the Winchesters realize that something more is going on.

Sam and Dean track down the missing Crowley and discover that he's now thoroughly addicted to human blood. Once they get him sober, the brothers go seeking the First Blade and find it in the possession of a former Man of Letters... who plans to add Dean to his collection.

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. He's unaware that Dean has actually gone out drinking to deal with the strain of unleashing the Mark of Cain.

Castriel 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 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 when the girl wants to go back to the vampires.

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. However, war is about to break out and the sides are drawn as the Winchesters discover that the original victim belonged to one of the clans.

Abaddon finally gets something that she can use as leverage against Crowley to force him to lure the Winchesters. 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 a suicide angel takes out an ice cream shop to kill one enemy angel, Sam and Dean investigate and discover that the target was one of Metatron's angels... and that Castiel may be responsible. Meanwhile, Metatron tries to consolidate his hold over the angel factions with promises that he will restore them to Heaven.

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, stripping him of his powers.