After a massive angel slaughter occurs, Sam and Dean arrive at the scene to investigate and are surprised to run into Castiel.
Sheriff Mills calls Sam and Dean for help investigating multiple murders in her small town.
Dean gets a call from an old friend named Sonny asking for help with a ghost that won't leave the home that Dean was sent to when he was younger.
A headline in the local newspaper about some disappearances in the area catches Castiel's (Misha Collins) eye, so he calls Dean (Jensen Ackles) to help him investigate the case.
While investigating two bizarre murders, Sam and Dean realize there is an eyewitness to both gruesome deaths – a German Sheppard.
Sam and Dean discover that the table in the Men of Letters house (the one that lit up like a Christmas Tree when the angels fell), has an ancient computer attached to it. They figure if they can get the computer on, they can track the angels. Who better to call for help than the best IT girl there is, Charlie Bradbury (guest star Felicia Day)? While moving the massive computer, they dislodge a hidden hexbag that unleashes a magical green-webbed wall. Sam and Dean break through it and discover the one and only Dorothy (guest star Tiio Horn) from Oz. She had trapped herself and the wicked witch (guest star Maya M) in the web years ago to stop the witch from finding the key that would open the gate that connected their world with Oz. With the wall broken, a massive and magical fight ensues that threatens to destroy the Men of Letters bunker.
After Ezekiel tells Dean a group of angels is hunting Castiel, he and Sam race to find their friend before the vengeful angels do. Meanwhile, a homeless Castiel is trying to make his way through the city and comes across some unexpected surprises.
Abaddon Rises! Dean shocks Sam by popping open the trunk of the Impala and showing him that he has kidnapped Crowley. Kevin freaks out when he sees the King of Hell, but Sam and Dean convince him that they need Crowley to find the demons on Earth. Meanwhile, Abaddon re-emerges and plans to take over Hell.
In the ninth season premiere, Dean is frantic after Sam collapses and the doctor tells Dean his brother won't make it. Desperate, Dean sends out an "All Points Bulletin" via prayer to every angel in the area – asking them to help his brother. In exchange, Dean will owe that angel a favor. Numerous angry angels race to find and kill Dean, but one, Ezekiel (guest star Tahmoh Penikett), gets to him first. Meanwhile, Sam fights for his life, facing some familiar demons in the struggle; and Castiel struggles to survive without powers.
Writer Adam Glass discusses Sam's Demon Trial
What must Sam, Dean and Castiel sacrifice to seal the gates of Hell? With Kevin's help, the Winchester brothers have one last play against Crowley.
As the third trial nears, Sam and Dean reunite with Castiel. They stumble upon an undiscovered film, which could be the key to the third trial.
After receiving a message from Kevin, Sam and Dean try to uncover the third trial. The boys make a discovery that sends them to a casino in Colorado.
Concerned about the toll the second trial took on Sam, Dean benches his brother until he heals up. Dean teaches Charlie to be a hunter-in-training.
Sam and Dean respond to Kevin, who is hearing Crowley's voice in his head. They later team up with a reaper to deal with the tablet's second trial.
Sam and Dean investigate some recent vampire kills and are surprised to learn that teenage hunter Krissy Chambers is involved.