The Apocalypse: the 66 seals, Lucifer and Michael

It's a few days before Halloween and Sam and Dean investigate two mysterious deaths in a small town. The brothers find hex bags and deduce a witch is sacrificing people to summon a dangerous demon named Samhain. Castiel arrives in town and tells Sam and Dean the freeing of Samhain is one of the Seals that will lead to freeing Lucifer, so Castiel has brought a specialist angel named Uriel to smite the entire town.

Someone found Lucifer's sword and is using it to kill angels. Castiel and Uriel have captured Alastair and ask Dean to use the torturing skills he learned in Hell to extract information from him so they can stop the murders. Sam is concerned Dean can't handle the job but Dean agrees to do it. However, when Alastair reveals some shocking information, Dean's world is shattered.

Dean and Bobby lock Sam in Bobby's panic room so he can detox from the demon blood. However, as Bobby sees more seals are being broken he tells Dean they should let Sam out to help them fight the impending apocalypse. Dean disagrees and goes to Castiel for help. Sam and Dean have a big blowout confrontation.

The apocalypse is coming, and Sam and Dean prepare for the fight in very different ways. Sam joins Ruby on a final run to kill Lilith, while Castiel and Zachariah tell Dean it's time to play his part in stopping Lucifer.

Picking up where the finale left off, Dean and Sam watch as the Devil emerges from Hell. The brothers and Bobby deal with the aftermath of Lucifer rising and the stunning news from Chuck the Prophet that Castiel was blown to bits by the archangels.

Castiel tells Sam and Dean that he is going to search for God, who will be able to defeat Lucifer. Bobby's old hunter friend, Rufus, is panicked about demons attacking his town, and begs Bobby for help. Sam and Dean arrive at the town and realize there is a spell over the townspeople, making them hallucinate that they are demons and causing them to kill one another.

Not sure he trusts himself anymore, Sam decides to give up hunting, but a late-night visitor won't let him off the hook that easily. Dean, intent on stopping the Apocalypse, continues hunting on his own and teams up with Castiel to find the Archangel Raphael, as Castiel believes Raphael knows God's location.

Sam tells Dean he wants to rejoin Dean in the battle of the Apocalypse, but Dean tells Sam that they are better off apart. Later, Dean awakens five years in the future in an abandoned city and is attacked by humans who have been infected with a demonic virus [Croatoan] that turns humans into Zombies. Zachariah appears to Dean and explains that this is the world that exists as a result of Dean saying no to helping the angels fight Lucifer. Dean meets up with Future Dean, who tells him that the virus is the Devil's endgame for destroying mankind.

Sam, Dean and Castiel track down the Colt and head off to find Lucifer to send him back to Hell. It's a hunters' reunion when the crew joins forces with Bobby, Ellen and Jo for what could be their last night on Earth.

The angels send Anna back in time to kill John and Mary Winchester before they can conceive Sam knowing that if Sam was never born then Lucifer won't be able to use him as his vessel. Castiel sends Sam and Dean back to 1978 so they can stop Anna, and the two brothers are reunited with their parents. Mary recognizes Dean as a hunter since he visited her in the past once before but tries to keep the truth from John.

Castiel helps Sam and Dean hunt down Cupid on Valentine's Day after townspeople start to kill each other for love. However, after Cupid tells them he's innocent, they discover Famine, one of the Four Horsemen of the Apocalypse, has arrived in town.

Sam and Dean are outnumbered by demons, but are saved at the last minute by Rob and his townspeople, who are aware of the Apocalypse, and have been training to fight and kill demons. The small town is very religious and Sam and Dean meet Pastor Gideon, who introduces them to his daughter Leah, whom he claims is a prophet. Leah tells the townspeople they must obey her orders if they want a spot in Heaven but when she starts turning the townspeople against each other in the name of the Lord, the brothers realize they must kill her.

Dean begins to think the only way to stop Lucifer is to say yes to Michael, but the angels decide they don't need him anymore. Dean, Sam and Castiel are horrified at the angels' new game plan and take on Zachariah to prevent an all out war on Earth. Meanwhile, a familiar face returns.

Sam and Dean are kidnapped by a group of gods, including Kali, Ganesh and Bladur and held hostage in a small hotel. The gods want to use Sam and Dean as bargaining chips to stop the Apocalypse, but Gabriel shows up and warns them that if Lucifer finds them he will kill them all. Unfortunately, one of the gods turns on the rest and Lucifer appears.

The demon Crowley tells Sam and Dean he can help them find the remaining Horsemen rings so they can trap Lucifer. The brothers are doubtful until Crowley leads them to Brady, the Handler for Pestilence and Death. However, Brady refuses to give up their locations and sets Pestilence after the Winchesters.

Crowley tells Bobby he will give him the location of Death, the fourth horseman, in exchange for his soul. Knowing Sam and Dean need that fourth ring to stop the Apocalypse, Bobby reluctantly agrees. Sam and Dean confront Pestilence, but he unleashes a deadly virus upon them, so Castiel must intervene on their behalf. Dean has a meeting with Death to discuss Lucifer, and an unholy alliance is formed at a very high price for Dean.

The entire season has been leading up to this showdown between good and evil. With the Apocalypse looming, Sam and Dean realize they are out of options and make heart-breaking decisions that will change their lives forever. A beloved character is killed.