It's four months later and Dean wakes up in a pine box. He's been freed from Hell. He has a joyful reunion with Sam and Bobby, but it isn't long before the three wonder what exactly pulled Dean from Hell and what it will want in return.
Sam and Dean are stunned when the spirits of Meg and Agent Henricksen appear and accuse the Winchesters of failing them. Although rattled, the brothers must pull together to save Bobby, who is too crippled with guilt to fight off the angry ghosts of the young children he couldn't save.
Dean is transported back in time and is shocked when he lands in Lawrence, Kansas. However, that shock turns to amazement after he runs into a young John Winchester and Mary who have just fallen in love. Dean isn't sure why he was sent back so he begins to enjoy the time with his parents and newfound grandfather who may be hiding a secret that is key to Sam and Dean's entire predicament.
Sam and Dean discover that Jack Montgomery a family man is turning into a Rugaru, a creature that starts as a human but changes into a flesh-eating monster.
Dean and Sam investigate several murders at Oktoberfest. The first victim was found with bite marks on her neck, much like a vampire would leave, while the second victim has wounds that look like a werewolf attack. After a mummy rises from his crypt, Dean determines that a shape-shifter demon is terrorizing the town as iconic monsters from the old Hollywood movies.
Sam and Dean investigate the mysterious deaths of several men who apparently dropped dead of fright. They visit one of the victims in the morgue, and Dean becomes infected with the illness which starts as a general anxiety, then moves on to full-blown terror that eventually stops the heart. Sam and Bobby must find the root of the disease before Dean dies and is sent back to Hell.
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.
Sam and Dean investigate a small town where the wishing well really works. A teddy bear comes to life, someone wins the lottery and the town geek gets a hot girlfriend. The brothers realize that while everyone is happy now, the end result will be disastrous.
Ruby tells Sam and Dean that a powerful demon named Alastair is searching for a girl named Anna who can hear the angels' conversations. The three set out to find Anna but once they do, Alastair attacks them and Ruby escapes with the girl.
Anna remembers her past and Sam and Dean finally understand why Castiel and Uriel want her dead. However, they disagree with the angels' orders and try to help Anna restore an important part of her past so she can be saved. Meanwhile, Alastair and his demons continue to close in on Anna and the brothers.