With the fate of the universe in their hands, Sam, Dean, Castiel, Crowley, and Rowena come up with a desperate plan to kill Amara. However, one of them must sacrifice their existence to do so.
The Winchesters ally with Chuck and Lucifer to destroy Amara, but discover that they need an even greater force to weaken her enough so that Chuck can strike the final blow.
God finally meets with the Winchesters, but he's not what they expected. Meanwhile, Amara requests a meeting with Dean, and the Winchesters set out to rescue Lucifer so that he can help God reimprison God's sister.
Sam and Dean travel to a town in Colorado where a fog is spreading the same madness that they ran into when they first encountered Amara. Meanwhile, Metatron is summoned to a meeting with God.
The Winchesters team up with two other hunters to take on the chitters, cicada spirits who possess humans so that they can reproduce.
While the Castiel-possessing Lucifer tries to take control of Heaven, Sam and Dean hear out Crowley on his plan to stop Amara.
Sam and Dean take on a pair of werewolves... and one of them manages to kill Sam. When Dean gets back to civilization, he kills himself in a desperate attempt to ge a Reaper's attention and make a deal to bring Sam back to life.
The new owners of a house accidentally break a seal, unleashing a creature that Bobby and Rufus trapped several years ago. Now Sam and Dean are working the same case, and have to save a new wave of coma victims before their bodies wither and die.
Sam and Dean decide to take a break and check out a wrestling tour. However, when a wrestler turns up dead, the brothers suspect demonic influence. Meanwhile, Crowley escapes from Hell with a little help from a friend and seeks out a weapon to kill Lucifer.
Sam locates an artifact capable of destroying Amara... that was lost at sea in 1943. The brothers convince Castiel--secretly Lucifer--to transport Dean back in time to recover the artifact.
A babysitter turns up dead on Valentine's Day, her heart ripped out, and the Winchesters soon discover that she was the victim of an Aramiac curse.
Sam and Dean meet with Jody and the two girls that she's housing: Alex and Claire. Claire has asked the brothers to help her investigate a series of recent disappearances, but Jody insists that there's nothing to them.
The Winchesters investigate two deaths at a retirement home, where the victims bashed their skulls in because of an intolerable screeching noise. They soon discover that the deaths are connected two deaths that occurred in Ireland 30 years ago. Meanwhile, Lucifer explores the world that he's been reborn into.
While Lucifer tries to convince Sam to let him out of the cage, Dean and Crowley come up with a plan to seal the Devil away permanently. Meanwhile, Castiel joins forces with another angel to confirm if Amara is dead or not.
While Dean tries to find Amara, Sam and Crowley convince Rowena to help them summon Lucifer from the cage so that Sam can try and persuade the Prince of Darkness to help them seal the Darkness away once more.
Sam is forced to relive his childhood when his imaginary friend Sully appears... and asks him to help solve the murder of another imaginary friend.
Sam and Dean team up with Sheriff Donna to stop a ghostly killer who possesses people who wear costumes.
While Castiel gets a lead on Metatron and interrogates him about the Darkness, Sam and Dean find Amara's location and try to sneak past Crowley's demons to get at the girl and kill her.
Sam and Dean investigate a double-murder at the B&B built in axe murderer Lizzie Borden's house, and discover what Amara has been doing since the last time they saw her.
The Winchesters decide to take a road trip to get out of the bunker, but find themselves in a life-or-death struggle with creatures intent on raising an army to fight the Darkness.
While Crowley tries to bend Amara to his will, Sam and Dean track down Rowena so that she can undo the attack dog spell that she cast on Castiel... before it kills him.
While Dean delivers Jenna and Amara to Jenna's grandmother, Sam tries to find a cure to the Rabid plague in Superior. Meanwhile, Hannah rescues Castiel from the other angels, and Crowley learns of the Darkness child.
After the Darkness passes them by, Dean begins to remember his encounter with the intelligence at the heart of their new foe. Meanwhile, the Darkness spreads, turning men into killers. Crowley escapes Castiel and makes plans to return to Hell, while Castiel beseeches his fellow angels to help him.