|While Dean sleeps, Sam slips out and Ruby picks him up. She asks if he's ready and he insists he is. Meanwhile, back in the hotel room Dean has a dream of Hell and then wakes up to find Castiel sitting next to him. The angel tells Dean that he has to "stop it" and touches Dean's forehead.
Dean wakes up on a park bench in a small town. He tries to make a call on his cell phone but gets no signal. He goes to a nearby diner and asks a patron where he is. The man tells him that he's in Lawrence, Kansas. Dean asks him where he can get reception for his cell phone and the man mistakes it for a Star Trek communicator,. then wonders when Dean says that Sonny and Cher broke up. Realizing something is wrong, Dean looks around and sees everyone wearing 1970s clothing and a newspaper date of April 30, 1973. An older man comes in and talks to Dean's new acquaintance, and refers to him as John Winchester. Dean realizes the person he's been talking to is his father and stares. Young John wonders if they know each other and Dean quickly denies it. As Young John leave, he stares at Dean for a moment and then departs.
Dean follows Young John and runs into Castiel, who explains that angels can bend time and Dean has to stop something. Castiel disappears before Dean can get an answer. Meanwhile, John is buying a VW van when Dean arrives and convinces him to buy the Impala instead. Introducing himself as Dean Van Halen, Dean asks if any weird activity has happened in town and creeps Young John out. Dean apologizes and takes off while Young John buys the Impala. He heads to his girlfriend's home and sees him get together with Young Mary. He follows them to a diner and watches as they argue over the fact that Mary's father is over-protective and doesn't want Mary involved with John. Mary steps away for a moment and Young John considers the engagement ring he has for her. Outside, Dean is watching when Mary grabs him and demands to know why he's watching them. He manages to subdue her… then notices the charm bracelet she's wearing and realizes that she's a Hunter.
Later, Young John drives Mary home and drops her off. Dean is waiting for her and says he's a Hunter as well. He insists on meeting her father Samuel and passes the initial test. Samuel orders him out, saying he doesn't trust Hunters. Mary's mother Deanna invites him to dinner, where he spars with Samuel. He claims he thought something was after Young John and Mary notices Samuel's disgusted look. Samuel admits John's a nice civilian but Deanna interrupts before they can argue. Samuel is working a job at the Whitshire farm where farmer Tom Wiltshire died after falling into his combine on a barren field. Dean suggests they team up but Samuel would rather work alone.
The next morning, Samuel goes to the farm disguised as a priest and takes Mary with him. as they go in, Mary notices a teenager leaning against a tree in the yard. He finds that Dean is already there, disguised as a priest. He's been talking with Beth Wiltshire, the dead man's husband. Things were normal on the form. However, Mary is talking to Tom's son Charlie, who admits that his father used to beat him. Charlie says that a stranger came a week ago and asked Charlie what he wanted, and Charlie told him he wanted the beatings to stop. The stranger said he'd come calling in 10 years, but Charlie thought he was a nutcase. Dean figures Charlie sold his soul to a demon without realizing it. Mary gets a description of the stranger: a man with yellow eyes.
Dean warns the Campbells they're all in danger and tracks down the Colt, which currently belongs to a Hunter named Daniel Elkins. Dean gets out his father's journal, which has a list of everyone who was in contact with the yellow-eyed demon. Included on the list is the next victim, Liddy Walsh: the yellow-eyed demon's next victim. The Whitshire Farm incident is listed and Samuel wonders how it could be in the book: Dean claims that his father could see the future. Samuel admits he thinks Dean is crazy but Dean insists he's going to kill the demon once and for all. Dean prepares to leave but talks to Mary and says he thinks she and Young John are destined to be together. He asks her what she sees in John and she admits he's nothing like a Hunter. She figures Young John is going to ask her to marry him and she plans to accept, even if she has to run away. She'll do anything to get away from the life of a Hunter, have a family, and be safe. She insists he won't let her children be raised like she was. Dean makes her promise to remember to not get out of bed on November 2, 1983. She agrees and Dean leaves.
Dean heads for the Hunter with the Colt but finds Castiel sitting in the car next to him. The angel explains that Dean has to handle this on his own, and Sam's not looking for him. Castiel explains that if Dean alters the future, all the people they saved will die. Dean admits he cares about those people, but he can't let his parents die. Castiel disappears on him again.
Dean breaks into Elkins' house but Elkins draws a shotgun on him. Dean points the Colt at him and asks to borrow it for a couple of days. Elkins considers the matter… and lets Dean go. Meanwhile, Samuel mentions to Mary that Dean plans to kill a demon that is targeting Liddy Walsh. Liddy is a friend of Mary's and Mary insists on going to help her.
Liddy is meeting with a man who offers to collect something from her in ten years in return for curing her father. His eyes glow yellow… and Samuel comes in and shoots him down. The demon knocks Samuels's gun away and slams him into a wall telekinetically. Mary tries to attack him with a knife but the demon holds her off and says he's impressed with her. Dean arrives with the Colt, which the demon recognizes. Mary breaks free and the demon escapes out of the host before Dean can shoot it.
Mary tells Dean about the demon's interest in her, and Samuel compliments Dean. However, Dean tells Samuel in private that if they don't kill the demon, Mary will die. When Samuel wonders how Dean knows what he knows, Dean explains that Mary is his mother and Dean is his grandson. He warns that now is the moment when the demon fixated on Mary, and they need to work together to stop it. Outside, Mary goes to Young John and asks him to take her away, now. They leave together.
Dean tries to convince Samuel who admits there's… something about Dean. He finally believes Dean and they go back to John's list. Samuel asks to see the Colt but Dean refuses. Samuel's eyes glow yellow and he telekinetically shoves Dean back against the wall, immobilizing him. The demon realizes that an angel is involved and that even though Dean doesn't have psychic abilities, a brother or sister does. Dean realizes that the deals the demon is making is to get the children and breed them into his personal master race. The demon is still interested in Mary, while Dean notices that Deanna is trying to get the Colt. Dean distracts the demon by asking what its plan is. The demon boasts that his endgame is a perfect plan but he doesn't plan to reveal it to Dean or the angels. Dean dares the demon to look into his eyes and realize that in the future Dean will kill him. The demon doesn't believe it and then takes out a knife and stabs Samuel's host body. Deanna screams and goes for the Colt, but the demon throws her away and then advances on her. Deanna crawls for the gun but the demon grabs her and breaks her neck. Dean gets the Colt and gets to Deanna, only to discover she's dead and the demon has left. He realizes where the demon is heading next.
Young John is parked with Mary and offers her the engagement ring. "Samuel" arrives and yanks her out of the car, then breaks Young John's neck when he interferes. The demon shows Mary the lethal wound on Samuel's body. Mary vows to kill him but the demon offers her a deal: he'll resurrect Young John if Mary grants him permission for him to visit in 10 years. He refuses to tell her for what but promises that no one will get hurt if no one interrupts him.
Dean arrives to find the demon kissing Mary. He draws the Colt but the demon leaves Samuel's body, leaving it dead on the road. John comes back to life and Dean realizes what's happened. Castiel appears and takes Dean back to the future, while John and Mary look at Samuel's dead body.
Dean wakes up in his bed with Castiel standing over him. He didn't change anything, but Castiel admits it was impossible for Dean to change his destiny. The angel sent Dean back to learn the truth, then admits they don't know what the demon's endgame is, or how it involves Sam. Castiel gives Dean Sam's location and warns that Sam is heading down a dangerous road. He tells Dean to stop Sam… or they will.