After a year apart, Sam and Dean are reunited in the Eighth Season premiere. After escaping from Purgatory with the help of a vampire named Benny, Dean heads straight for Sam, but the reunion isn't exactly everything he imagined it would be. Although Sam drops everything to join his brother, leaving the life he had grown accustomed to enjoy turns out to be harder than he imagined. In the meantime, Benny’s help turns out to be more than what Dean bargained for. As the brothers struggle with their unexpected reunion, they make a shocking discovery that could lead them on a deeply personal mission to settle old scores. If only they could agree – is this a “family business” or isn’t it?
One Year Later Dean’s escaped from Purgatory, though Castiel is nowhere to be found. However, Dean isn’t alone. He’s returned with a mysterious comrade-in-arms whose reason for escape is perhaps more than Dean bargained for. Meanwhile, Sam finds himself reconciling the life he discovered while Dean was gone with Dean’s sudden reappearance. As the boys struggle with their unexpected reunion, they make a shocking discovery that could lead them on a deeply personal mission to settle old scores. If only they could agree – is this a “family business” or isn’t it?.
Kevin talks Sam and Dean into checking in on his mother. When they arrive, they see that Crowley has surrounded her with demons so they rescue her and take her along on their quest to find the tablet. However, they soon discover Kevin wasn’t kidding when he said his mother was a strong-willed woman after she tries to take on Crowley.
Sam and Dean investigate a string of unusual murders where the victims were all recipients of organs from the same donor. The killer is captured, but things become even more complicated when the brothers find their killer in a trance mumbling an ancient prayer.
Sam and Dean investigate a bizarre murder in a college town. Close on the tail of their suspect, they bust into an apartment to find two dead bodies and a laptop cued up to some disturbing video footage. The footage begins with Brian, Mike and Kate hearing about an unusual animal attack in their town and the rest of the story is revealed through their eyes. Sam and Dean become unknowing participants in a unique student film.
After Benny gets brutally beat up by some vampires, he calls Dean for help. Dean abruptly packs up and tells a confused Sam that he’s taking a "personal day." Benny confesses that he’s going after his Maker so Dean offers to help, flashing back on the many times Benny helped him and Castiel in Purgatory. Meanwhile, Sam uses his solo time to reflect on the life he left behind with Amelia. However, when things go bad for Dean and Benny, Dean calls Sam for help, which makes everything very complicated.
Sam and Dean investigate a murder and find Garth is already on the case. Dean is not happy to learn that Garth has assumed Bobby’s duties, but Garth points out that both Sam and Dean have been missing for the last year and someone needed to do it. They guys discover an "avenging ghost" is responsible for the murders and they need to find the source before the killings starts again.
Sam and Dean are stunned when Castiel suddenly appears back on Earth with no memory of how he escaped from Purgatory. Meanwhile, Mrs. Tran enlists a witch to concoct a demon bomb, but the witch double crosses Mrs. Tran and turns her and Kevin over to Crowley.
Castiel tells Sam and Dean that he’s decided to become a hunter like them. Sam and Dean aren’t sold on the idea but agree to investigate a case Cas found where a man’s heart literally burst through his chest. The guys discover there has been more than one odd murder in the small town and all of them resemble cartoon deaths.
Sam asks a hunter named Martin to keep an eye on Benny without telling Dean. However, when Martin tells Sam there was a vampire kill and he thinks Benny is responsible, Dean defends his friend. When Martin decides to take things into his own hands, things get messy and Dean is forced to make a very hard decision.
Naomi tells Castiel that Crowley is holding an angel captive and Castiel must rescue him before Crowley finds out their secrets. Castiel turns to Dean for help. Meanwhile, Sam meets with Amelia who asks him to make a choice: stay with her or leave and never contact her again.
Sam and Dean investigate the mysterious deaths of two LARPers (Live Action Role Playing) who were playing a game entitled Moondoor. The guys are thrilled to discover the Queen of Moondoor is none other than Charlie. The three learn that a fairy has been commandeered to harm people and the only way to stop her is to find her master.
Sam and Dean are stunned when a man who claims to be Henry Winchester, their grandfather, suddenly appears in their hotel room demanding to know where he can find John Winchester. Henry has time-traveled to stop a demon named Abbadon and was looking for John’s help. Through Henry, Sam and Dean learn more about their father and the Winchester blood line.
Sam and Dean investigate the death of Rabbi Bass, who spontaneously combusted. The case becomes ever more confusing when they learn that the Rabbi was researching Nazi Necromancers. Sam and Dean are attacked by a Golem who turns out to belong to the Rabbi’s grandson, Aaron. The key to the case lies with the Golem but Aaron doesn’t know how to control him, which leaves everyone in danger.
Kevin deciphers the tablet and figures out how to close the gates of Hell. He tells Sam and Dean that according to the tablet one person must face a series of three tests designed by God. The first one – kill a hellhound. Sam and Dean argue over who should complete the trials.
A police officer named James, who turned to witchcraft after working a case with Sam and Dean, is plagued by nightmares in which he murders innocent people. However, when the murders actually happen, Sam and Dean are called in by James’s "familiar" to help -- but the brothers aren’t sure they want to save a witch.
Sam and Dean are stumped when they investigate a possible zombie case where an amnesiac man dies and then revives himself once a day. After the guy is attacked by the goddess Artemis, Sam and Dean realize he’s not a zombie but instead a God, more specifically, Prometheus.
Castiel reappears in Sam and Dean’s life and tells them Crowley has unleashed several demons into a small town. The demons are looking for Lucifer’s Crypt, which holds a valuable asset, but Castiel lies to Sam and Dean about what it is. While interrogating a demon, the three discover Crowley has been torturing Meg, who knows the exact location of the crypt. Sam and Meg fight to hold Crowley off while Dean and Castiel go in search of the crypt.
Sam and Dean investigate some recent vampire kills and are surprised to learn Krissy Chambers is involved. They find Krissy and learn her father was killed and she’s been taken in by a man named Victor, who has taken in a group of orphan kids to teach them how to hunt. Victor is helping the teenagers find the vampires who took their parents so they can get revenge. Sam is intrigued by Victor’s method of giving the teenagers a home life as well as a hunting life, but Dean is suspicious of Victor’s motives.
Sam and Dean respond to a call from Kevin, who is terrified after hearing Crowley's voice in his head. After hearing Kevin's news, Sam and Dean team up with a reaper named Ajay, who helps them deal with the second trial from the Tablet. Meanwhile, Dean receives a visit from Naomi and realizes he must find Benny and ask for a huge favor.
Concerned about the physical toll the second trial took on Sam, Dean benches his brother from hunting until he heals up. So, when geektastic hacker Charlie stumbles upon a case and finds the boys, Dean decides it's time to teach Charlie how to be a hunter-in-training. While happy to see "her highness," the boys suspect Charlie is hiding something; a secret that could get her killed.
When Sam and Dean receive a distressing video message from Kevin Tran, they set about trying to uncover the Third Trial. The boys make a discovery that sends them to a casino in Colorado, to find a mysterious recluse who may be able to fill in the holes in Kevin’s research. Meanwhile, Crowley is on a winning streak. Castiel tries to elude Naomi and the angels hunting him.
Sam and Dean reunite with Castiel. Digging through the Men of Letters' files, they stumble upon an undiscovered film which could be the key to the third trial. Metatron enlists Cass to mull over problems at home. Meanwhile, Crowley digs into Sam and Dean's past.
With Crowley poised to undo all the good they’ve ever done as hunters, Sam and Dean find themselves cornered. But with Kevin's help, the Winchester brothers bound into one last play against The Demon King. Metatron initiates a plan with Castiel to take on Naomi and the bureaucracy of Heaven.