One Year Later, and 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.
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.
After Benny gets brutally beat up by vampires, he calls Dean for help who abruptly packs up and tells a confused Sam that he’s taking a personal day. Meanwhile, Sam uses his solo time to reflect on the life he left behind with Amelia.
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 someone had to pick up the slack.
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.
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 that all the deaths resemble cartoon deaths.
Sam asks a hunter named Martin to keep an eye on Benny without telling Dean. However, when Martin tells Sam and Dean there was a vampire kill and that Benny is responsible, Dean defends his friend.
After Naomi orders Castiel to rescue an angel being held captive by Crowley, he 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 who were playing a game titled Moondoor. The guys are thrilled to discover that the Queen of Moondoor is none other than Charlie.
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, their father.
Sam and Dean investigate the death of Rabbi Bass, who appears to have spontaneously combusted. The case becomes even more confusing when they learn that the Rabbi was researching Nazi Necromancers.
Kevin deciphers the demon 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 trials, and the first one is to kill a hellhound.
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.
Sam and Dean are stumped when they investigate a possible zombie case where an amnesiac man dies and then revives himself every day. After the man is attacked by the goddess Artemis, Sam and Dean realize he’s not a zombie.
Castiel reappears in Sam and Dean’s life and tells them Crowley has unleashed several demons into a small town in order to find Lucifer’s Crypt, which holds a valuable relicts. While interrogating a demon, the three discover Crowley has been torturing Meg, who knows the location 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.
Kevin is terrified. He has started hearing Crowley's voice in his head and calls Sam and Dean for help. After hearing Kevin's news, Sam and Dean team up with a reaper named Ajay, who helps them with the second trial from the demon tablet.
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 Bradbury stumbles upon a case, Dean decides it's time to teach Charlie how to be a hunter-in-training.
When Sam and Dean receive a distressing video message from Kevin Tran, they set out trying to uncover the third trial. The boys make a discovery that sends them to a casino in Colorado where they find a mysterious recluse who may be able to fill in the holes in Kevin’s research. Meanwhile, Castiel tries to elude Naomi and the angels hunting him.
Sam and Dean are reunited with Castiel as they are digging through the Men of Letters' files. They stumble upon an film which could be the key to completing the third trial. Metatron enlists Cass to mull over problems at home.
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 Winchesters ready themselves for one last play against the King of Hell. Metatron initiates a plan with Castiel to take on Naomi and the bureaucracy of Heaven.
