After Sam collapses, his doctor tells a frantic Dean that his brother is dying; Dean tries to make a deal with an angel.
Sam is shocked when he learns that Dean kidnapped Crowley; Abaddon re-emerges with plans to take over hell.
Dean and Sam try to protect Castiel from a group of angels; Castiel encounters surprises as he makes his way through the city.
Dean and Sam find an ancient computer which they hope to use to track angels; a magical green-webbed wall is released.
Dean is afflicted with an inconvenient side effect after he and Sam cast a spell to communicate with a canine murder witness.
Castiel calls Dean when he reads about a disappearance in the area; Dean tries to keep Sam distracted by asking him and Kevin to decipher the tablet with Crowley.
An old friend calls Dean and asks for help finding a ghost; Sam is stunned when information about Dean's past comes to light.
Sheriff Mills asks Dean and Sam for help investigating several murders in her town; when it is discovered that four victims belonged to a chastity group, Dean goes undercover.
As Dean and Sam investigate the scene of a massive angel slaughter, they run into Castiel; Dean considers telling Sam the truth.
Dean seeks revenge on the angel that killed Kevin; Castiel has a plan to get Sam to expel Gadreel by separating his brain from the angel's.
Crowley needs Dean's help finding the only blade that can take down Abbadon; Castiel notices some grace left inside Sam.
Dean and Sam find out that Garth is in the hospital and decide to go check on him; when Garth runs away from the brothers, they investigate the reason behind his disappearance.
Dean and Sam go under cover at a fancy day spa to investigate recent murders that left the victims hundreds of pounds lighter after their death.
Dean and Sam learn that the Men of Letters' bunker is haunted; an investigation reveals a storage facility in which demons have been keeping something important.
The last photograph of a dead teenager reveals a ghostly figure in the background; the brothers learn that famous supernaturalists are also investigating the teen's death.
Crowley promises to find the first blade, but ends up falling off the wagon and asks Sam and Dean for help; Abaddon learns that the brothers are looking for the blade.
While Dean deals with the after effects of the Mark of Cain, Sam learns of a case in which straight-laced people turn into violent killers.
When Castiel rejects Metatron's offer to join forces, a surprising plan is set in motion; Gadreel is apprehended.
When Sheriff Mills calls Sam and Dean after a run-in with a vampire, they discover the vampires kidnapped a girl to use as bait to lure human victims.
Dean and Sam learn that mafialike monster families are running the underbelly of Chicago; Ennis refuses to listen to a warning from the brothers.
Castiel asks Dean and Sam to help interrogate one of Metatron's angels; Abaddon reveals her shocking bargaining chip when Crowley refuses to help kill the Winchester brothers.
Castiel needs Sam and Dean's help after a massive attack on the angels; Sam worries about Dean's eagerness to use the first blade; a conspiracy is uncovered.