Dean and Sam are faced with their biggest threat: the darkness that has been unleashed; Castiel experiences the impact of Rowena's spell and remembers his battle with Crowley.
Jenna winds up in a dangerous situation and calls Dean for help, leaving Sam to deal with monsters on his own.
While Rowena endeavors to protect herself against the Winchesters, Sam and Dean pursue a missing child connected to the Darkness; Castiel struggles to heal; Crowley looks to use the Darkness to his advantage.
Sam and Dean's road trip to fight monsters and demons is chronicled entirely from the Impala's perspective.
Sam and Dean investigate a series of murders at a bed and breakfast that used to be Lizzie Borden's home, but when a man says he saw a little girl hanging around near the time of the murders, the Winchesters suspect Amara is responsible.
Castiel asks Metatron to help stop the Darkness, but Metatron is happy with his new life and reluctant to assist; Crowley's hold on Amara loosens.
Sheriff Donna asks Dean and Sam for help with a murder that has supernatural elements; Sam's visions continue.
Sam is surprised when his childhood imaginary friend, Sully, suddenly shows up and Dean can see him too.
Amara issues a shocking challenge, unleashing her power on the local residents; Dean tries to make sense of the hold Amara has on him; Sam and Crowley come up with a potentially disastrous plan.
Lucifer offers Sam a costly way out of the cage; Dean and Castiel investigate the angel smiting that might have killed Amara.
When people are met with violent deaths after listening to a mysterious song, Dean and Sam investigate.
Claire thinks recent murders in town are supernatural and asks Sam and Dean for help; Jody Mills reveals that Claire has been attacking people and accusing them of being monsters.
While investigating a set of murders on Valentine's Day, Sam and Dean find they are dealing with an ancient curse that causes victims, once kissed by it, to die.
When Dean needs to go back in time to find a weapon that is powerful enough to defeat Amara (Emily Swallow), he turns to Castiel/Lucifer for help.
Dean and Sam decide to take a break and attend the funeral of a wrestler they were fans of as kids; when another wrestler turns up dead, the brothers quickly return to work.
After an insidious creature is accidentally released into an old house, leaving a mother and child in a coma, the Winchesters must reach into the past to devise a plan to catch the monster before it kills someone.
When Sam gets shot while rescuing two victims from a pair of werewolves, Dean must get everyone out and try to evade the pack that is pursuing them.
Lucifer tries to assert himself into heaven; Crowley tells Sam and Dean they must take down Amara (guest star Emily Swallow).
Sam and Dean go to a small town in Colorado to meet two hunters who have a personal vendetta against monsters that appear once in a generation and cause mysterious disappearances.
Amara causes a small town to go mad when she places a dark fog upon it; Sam, Dean and the sheriff try to protect the town, but the old remedy fails.
Concerned for Castiel, Dean and Sam devise a plan to rescue Lucifer from Amara's (Emily Swallow) clutches.
Sam and Dean come up against the biggest challenge they have ever faced; Rowena decides to make her move.