We see Anna as she realized she was an angel, and then admitting she has a price on her head because she disobeyed. She’s taken back to heaven. We see Dean transported to 1973 to try to stop what happened then to set future events in motion, especially the death of Mary ten years later. But he can't stop it, and Castiel tells Dean that destiny cannot be changed.
Dean says, “Oh, I take it back – I love the devil,” as a stripper in a little devil outfit dances to one of Dean’s favorite two songs, “Cherry Pie.” She’s joined by another sexy girl in fluffy angel wings, and Dean’s in heaven. Until the girls part to reveal Anna. Dean is embarrassed as she asks if this is what he dreams about. Then she tells him she’s been trying to find him but can’t, of course, because of the sigil carved in his and Sam’s ribs. So she tells him where to meet her.
At the warehouse rendezvous, it’s Castiel who shows up to confront Anna. He didn’t trust her and wouldn’t let the Winchesters come. They have a bit of a standoff with big knives, but then Anna says she wants to help. And the way she wants to help? “Sam Winchester must die,” she says. Cas argues that there must be another way, but Anna points out that nothing they have tried so far has worked – they can’t kill Lucifer with the Colt, and Cas can’t find God – so it’s time to go to the source. But Cas puts his foot down: “You come near Sam Winchester, and I’ll kill you.” Anna vanishes. She reappears in 1978.
Meanwhile, in a motel room, Cas does a ritual to find Anna, sees her in 1978, and explains to Dean and Sam that Anna plans to kill their parents so that Sam can never be born (and neither can Dean, of course). The Winchesters insist on going with Cas, even though the angel, now cut off from heaven, knows it will weaken him tremendously. When they arrive in 1978, Cas is throwing up blood. Sam and Dean put him in a hotel room to regain his strength and go find the young John and Mary.
Mary remembers Dean all too well and doesn’t want him there – she has a normal life now, she claims. But John is all too happy to meet cousins of hers, which is who the boys pretend to be. Sam is completely astonished, meeting his own mother. Despite Sam’s goofiness and the obvious tension between Dean and Mary, John invites them to stay for dinner. While he goes to answer the phone, Dean and Sam talk to Mary and tell her something is after her and John, and all they have to leave. Sam blurts out that it’s an angel, and Dean describes that angels are more powerful than demons – and they are bigger dicks. By the time they convince Mary, John is gone – the call he took was supposedly from his boss, asking him to come to the shop: it was really Anna disguising her voice.
John arrives at the shop and finds his boss dead, with his eyes burnt out. Anna tosses John around a bit, but the cavalry arrives, and Dean tries to stab Anna. She tosses him aside, and Mary takes over, stabbing her with a tire-iron. Not so easy to kill an angel, Anna tells her, but it’s just enough to distract one, Sam chimes in, as he activates the angel-banishing sigil he’s drawn on the wall. Anna is gone again.
In the Impala, the boys and Mary tell John about monsters being real and how they hunt them. He takes it fairly well but ends the conversation by telling them all to just shut up or he’ll stop the car – just like a dad – and Dean quips, “Wow, awkward family road trip.”
They come to a house in the country that Mary says has been in the family for years – and it is equipped for hunters. However, none of the devil’s traps and salt will help against angels, so Dean and Sam show them some of their new tricks, like the sigil and the oil. John’s is grudgingly all on board with being helpful and volunteers to draw the sigil in human blood, which reminds Dean of the father he knew growing up.
Sam and John have a heart-to-heart while they prep the house. Both the boys and Mary have now told him they were brought up into hunting, and John is appalled about who would do such a thing to a child. “Your father was supposed to protect you,” he tells Sam, who answers that his father died trying to do just that. Sam tells young John the story about his father’s love for his mother, and how he turned to hunting after she was killed. He says his father died before Sam had a chance to tell him he understands, forgives him, and loves him.
Meanwhile, a younger Uriel appears and joins forces with Anna to kill the humans she says must die.
In a moment of downtime, Mary asks Dean to explain why an angel wants her dead. Of course, he does not want to tell her. But to keep her from leaving, he blurts out that he’s her son, from the year 2010, and repeats that the yellow-eyed demon will kill her on November 2, 1983, so she must not go into the nursery that night. Sam joins them, and they try to convince her to leave John – that’s they are fine with never being born – but she tells them she can’t. Not now. She’s pregnant.
Suddenly John rushes in to tell them the sigils are smudged. The oil evaporates, the glass from the windows blows inward, and they all shield their ears from the piercing shriek as Anna and Uriel arrive. Anna throws John backwards, straight through a window, to land unconscious outside. She throws Dean aside and stabs Sam, then goes after Mary. Outside, John is illuminated by a bright white light. Just as Anna is about to do away with Mary, John walks back in – as Michael’s vessel! He fries Anna and then snaps his fingers to make Uriel disappear. Dean tells him to fix Sam, but Michael wants to talk first. Just like all the other angels (except Cas) he explains how everything is destined, telling Dean that free will is just an illusion. Dean asks how he took on John as his vessel if Dean’s supposed to be “it,” and Michael explains that it’s in the bloodline – stretching all the way back to Cain and Abel. “Awesome,” Dean says, “Six degrees of Heaven Bacon.” John said yes to Michael when Michael said he could save his wife who was about to be killed. Michael tells Dean he will wipe John and Mary’s memories, and he does fix Sam and sends him back home. He then tells Dean they’ll be seeing each other again soon before sending him back as well.
Back in 2010 at a motel, Cas materializes right behind them, very weak but alive. Sam wonders whether what everyone’s been saying is right, that eventually they will both give in. Dean tells him it won’t happen.
Back in 1978, a very pregnant Mary shows John the little ceramic angel she found at a yard sale, and for the first time tells an unborn Dean that angels are watching over him.