Four months after the season three finale, Dean wakes up in his own grave and claws his way out. He and Bobby meet up with Sam at a motel, where an overwhelmed Sam joyously reunites with Dean. While trying to figure out how Dean returned from Hell, Dean and Bobby confront the being who revived him, Castiel, an angel who was ordered by the Archangel Michael to raise Dean from the fires of hell and resurrect Dean. They discover that this happened because the angels need Dean and Sam's help to stop Lilith, who is breaking the 66 Seals of God. Once the Seals are all broken, Lucifer, the first fallen angel and chief adversary in the war of angels and demons, will be freed from Hell, bringing the Apocalypse upon the Earth. It is also revealed that Lucifer spawned all of the demons starting with Lilith who is now active. Castiel develops a friendship with Dean and helps him understand the upcoming events. Castiel also reveals the Winchesters' past and shows Dean the connection between the now deceased Demon Azazel and his family. He reveals that Dean's mom was a hunter and working cases around the time Azazel was making crossroad deals in 1973. She and her hunter family, the Campbells, tracked the yellow eyed Demon down and eventually the Demon was stopped, but not before the Demon possessed and killed Mary's father and mother and killed her then boyfriend John Winchester. Shockingly, Azazel makes a deal with Mary to bring back John in exchange for certain debts owed 10 years later. When Mary protests over the cost being her soul, Azazel says that he doesn't need her soul- just a favor years later. Dean is shocked that Mary's deal resulted in he and his brother's permanent lives as hunters.