|Season 5 begins where Season 4 finished, with the freeing of Lucifer and the beginning of the Apocalypse. As Sam and Dean are saved from obliteration created by Lucifer's rise by an unknown force, they look to the prophet Chuck for help. With Castiel seemingly out of the picture after being killed in the Season 4 finale, the boys go in search of the sword of the Archangel Michael. They run into Zachariah and are there told that Dean is in fact the sword of Michael, and is the only one who can defeat Lucifer by allowing Michael to use him as his vessel. Castiel is revealed to be alive and goes in search of God after assisting the boys in escaping from Zachariah. Meanwhile, Lucifer finds his first vessel.
The Season then introduces the notion of the Four Horsemen of the Apocalypse(War, Famine, Pestilence and most importantly, Death). Each of which carries a ring of great power necessary when re-opening the cage in which Lucifer had escaped from. Lucifer summons Death to Earth as a necessary step in his apocalyptic plans. The brothers arrive with the colt during the summoning where dean shoots Lucifer with a bullet to the brain, which serves to do nothing as Lucifer reveals he is one of few that the Colt cannot kill. The brothers encounter further problems as the fallen angel, Anna, attempts to prevent the apocalypse through not only attempting to kill Sam, but then travelling back in time to kill John and Mary to prevent his conception.
Zachariah gives up on using Dean as a vessel for Michael and instead revives their half-brother, Adam, to become Michael's vessel. In Lucifer's pursuit of Sam, a fight ensues between him and a group of pagan gods and then his angel sibling, Gabriel. In 'The Devil You Know', Sam's plan to trick Lucifer into possessing him and jumping into the cage is revealed and is the route they eventually take. Dean receives the final ring from Death who willingly gives it over as a result of his hatred for Lucifer.
The season climaxes with Lucifer possessing Sam and Sam being unable to take back control, therefore the plan fails and all seems lost. Lucifer and Michael meet for their final showdown in Stull Cemetery only for Dean to turn up in one last attempt to wrestle back control for Sam. Castiel turns up and banishes Michael with holy fire and in a bout of rage, Lucifer kills Castiel and then Bobby. With all seeming lost, the memories of the Impala allow for Sam to wrestle back control and as Michael returns, Sam takes both Lucifer and Michael into the cage.
The Season ends with Castiel being resurrected and him then bringing Bobby back from the dead, and then cut scenes with Dean to begin living a normal life with Ben and Lisa.