The episode starts deep in the woods with Dean chasing after a man, whom he’s clearly shot. But when the hunter catches up with the guy he is revealed to be a witch. As Dean closes in on the witch, the man uses a symbol he drew on a tree to blast Dean with some sort of spell and the older Winchester brother is knocked out cold.
Dean wakes up the next morning in the woods and his phone is broken. He finds his way to a path and borrows a cell from a jogger to call Sam. After surveying the area he tells his brother to meet him for breakfast at a nearby waffle place.
Over a breakfast of plenty of waffles, Dean explains that he can’t remember anything from the night before. The brothers assume he had an ‘epic night’. But it’s not just the previous night that he can’t recall. Dean can’t remember the “devil baby mama drama” or the case that he and Sam are currently working.When they go to leave to continue working their case, he’s confronted by a woman who slaps him in the face for not remembering her.
Sam and Dean head to the morgue to talk with the medical examiner. He reveals that the victim’s stomach was filled with cash and that’s what killed him. But that’s not the only thing the brother’s discover. There was also a hex bag, which means that a witch was involved.
When they leave, Dean forgets how to drive Baby and then forgets his own name, leading Sam to realize that this is more than just the aftermath of a wild night out.
Back at their motel, Sam quizzes his big brother. When Dean fails to remember all the names of the members of Bon Jovi or the word for lamp (calling it a “light-stick”), Sam calls Rowena for help. She’s currently in the middle of a poker game, and using her magic to win it. She tells him that there is a spell that slowly erases the victim's memories and that the key to breaking it is to kill the witch.
Retracing their steps from the day before, Sam recalls that he and Dean had split up when Sam went to do research and Dean went to grab food. So they start looking around at the places in the area where he could have gone. At one place, they run into the woman who slapped Dean. She works there and after Sam explains (lies) that Dean was roofied at the bar and can’t remember anything, the woman describes what happened. It seems Dean spent his night drinking, riding Larry (the mechanical bull) and hooking up with the waitress. Then Dean apparently had left the bar in a hurry. The brothers check the security tapes. They see Dean confront a man out back the bar. Dean doesn’t remember any of it, and tries to read his own lips on the security tapes. He ends up ‘translating’ “now salsa you mittens” before he remembers that he can’t read lips. When they watch Dean shoot at the guy, the older brother is surprised to see that he knows how to shoot a gun. Sam however, recognizes the man from a picture on the victim’s wall.
The brothers head into the woods to track where the man went and while they are walking Sam has to give Dean ‘the talk’. He informs the older Winchester that the supernatural is all real. And that they kill monsters. Dean thinks the whole thing is awesome and that they have the best jobs ever.But then Sam and Dean stumble upon the witch who hexed Dean and discover that he’s already dead. A dead witch should’ve broken the spell, but it didn’t. Sam asks Rowena to come meet up with them.
Rowena, figures out which family they’re dealing with the instant she sees the archaic form of Celtic used to hex Dean. She tells the brothers that the witches came over from the old world about a century ago and own a powerful spell book called the Black Grimoire. For many years witches would live with them to study their secrets, but then the family was wiped out by hunters. Rowena thought were all dead, but now it’s apparent some found a way to survive all these years. She tells Sam, while Dean sits in the background watching Scooby-Doo, that they need to find the Black Grimoire in order to fix Dean. And they’ll need to hurry because as the spell continues, Dean will eventually forget everything, including how to swallow... and then he’ll die. Hearing this, Dean comments, “Sucks for that guy!”
Before Sam heads off to find the Black Grimoire, he tells Dean their whole life story and that he’s forgetting it all. Then the younger sibling confesses to Rowena, “I’ve seen my brother die, but watching him become not him? This might actually be worse.”
Meanwhile, Dean stands in front of the bathroom mirror reciting, “My name is Dean Winchester. Sam is my brother. Mary Winchester is my mom. And Cas is my best friend.” Slowly the speech breaks down until he forgets even his own name.
Sam goes to confront the witches, leaving Rowena to watch over Dean. Rowena opens up to Dean, revealing that she was run out of her homeland by the British Men of Letters, and then ended up going to live with the very people they’re currently hunting. Only, they threw her out when they felt her magic wasn’t up to snuff. She then confesses about how seeing God and Amara bicker made her wonder if there was any hope for her. When Dean inquires as to why she’s sharing all of this (as he sits and plays with one of her voodoo dolls) she comments that it’s okay to tell him because he won’t remember.
But their conversation is interrupted when Sam calls. He’s made it inside the house, but before he can get to the book they need, Katrina and Boyd, the last two of the witch family, knock him out and tie him up. Their plan is to use Sam’s body to bring their dead brother back.
After the call that ended abruptly, Rowena takes Dean and makes her way to rescue Sam. She leaves him in the Impala and goes into the house. There, Katrina recognizes her and after a bit of insults, they fight.
Dean wakes in the car to see a Post-It that tells him to stay there. He does, but not for long. He gets out and sees a note on the trunk that says ‘open me’. Inside, the grenade launcher has a big “NO!” Post-It on it, but the witch killing bullets that he needs to use and a gun are clearly marked with more sticky notes.
Dean goes into the house and shoots Katrina, saving Rowena’s life. Then he sees two guys running down the stairs. With no memory, he’s not sure who to kill. Sam quickly identifies himself as Dean’s brother and points out the witch. Dean shoots the last of the witch family.Rowena is then able to fix Dean (although at first Dean pranks Sam by pretending to still not recognize him) and then she hits the road… after Sam confiscates the Black Grimoire.
As the brothers leave, Sam admits that he was a bit jealous of Dean at first because he didn’t have to carry the weight of the world on his shoulders due to painful memories. But Dean objects that if losing the bad stuff meant losing everything else important as well, it wouldn’t be worth it.
The episode ends with scenes of Dean riding the bull intersected with clips of his memory-less day.