Dean and Sam Winchester are two brothers with a special talent. Well-versed in the supernatural after their father became convinced that their mother was captured by unholy spirits, Dean and Sam dedicated their young lives to hunting down these otherworldly terrors. But adulthood saw Sam drift away from these preternatural activities, instead choosing to settle down in a life of domestic bliss with his girlfriend. But when the Winchesters' dad goes missing, both Dean and Sam know what they have to do - leading to some epic cross-country trips as the brothers try to find their father.
Sam and Dean investigate recent murders where the victims were hundreds of pounds lighter after their deaths. Suspecting witches, the two go undercover at a fancy day spa that all of the victims had attended for weight loss. While Sam is hired as a fitness instructor, Dean takes kitchen duty. After Dean swipes some tainted food and passes out, the guys realize someone is drugging the guests and literally sucking all of the fat out of them until they die.
After finding out that Garth is in the hospital, Sam and Dean go to check on him. Still carrying the guilt over Kevin, Dean lays into Garth about disappearing and demands to know where he's been. Garth makes an excuse and then hightails it away from the guys. Confused as to why Garth would run from them, Sam and Dean do some investigating and are stunned by what they find.
Looking to reclaim his place as King of Hell, Crowley asks Dean for help finding "The First Blade," the only blade that can kill Abbadon. Knowing he owes Crowley a favor for helping Sam, and also wanting Abaddon dead himself, Dean reluctantly agrees and the two set off on a road trip. However, Dean and Crowley are completely unprepared when they find out who has the blade - Cain, the first son. Meanwhile, Sam is back at the bunker with Castiel who notices there is some leftover grace inside Sam. If they can extract it, they can use the grace to track Gadreel. The only problem is the procedure may do permanent damage to Sam.
Dean is devastated after Kevin's death and vows to find the angel that killed him, not only to free Sam, but to seek revenge. Castiel arrives at the bunker and suggests they try to separate Sam's brain from the angel's so they can talk to Sam and have him expel Gadreel. However, there's one small problem: the only person who knows how to do that is Crowley.
After a massive angel slaughter occurs, Sam and Dean arrive at the scene to investigate and are surprised to run into Castiel. While investigating, Castiel is captured and tortured. Meanwhile, Dean questions Ezekiel's demands and wonders if it might be time to tell Sam the truth.