Bristol, Rhode Island
One year ago, Sam shots someone as Samuel looks on. They then leave the house and Sam says that his wounded arm will hold out until they leave the town. As they drive away, a police car comes up behind them and pulls them over. Deputy Atkins pulls them out, believing that they're FBI agents, and tells them that he can't raise Sheriff Dobbs or anyone else on the phone. He notices that Sam's arm is bleeding, and orders them in the car. Sam refuses and brutally beats him unconscious while Samuel looks on. They then drive away.
At the motel, Sam is catching up on the news when Dean arrives. Bobby hasn't picked up anything on the Mother of All yet. Sam gets a text message from an unidentified caller with latitude and longitude. They're for Bristol, Rhode Island, and Sam confirms that three women have disappeared into thin air there in the last week. There's no answer to the phone call, but Sam is eager to go. Dean advises against it, but Sam insists that they can't just ignore the missing girls.
As the brothers pull into Bristol, Sam gets brief flashes of being in the town with Samuel. They stop at a diner and determine that the missing women had nothing in common. As Dean goes to the restroom, a woman approaches Sam and recognizes him from when he was posing as a Federal agent. The woman, Debra Harris, figures that he's back because the disappearances have started again, and Sam plays along. Meanwhile, Dean leaves the restroom and sees Sam in a photo for an eating contest. He interrupts Sam before he can get in further, and they say goodbye to the woman and her husband. As she leaves, Sam remembers having sex with her on a bathroom sink. Dean picks up on Debra's glance, and they wonder what happened a year ago.
At their motel, Sam insists that they stay. He's confirmed that five m en turned up missing a year ago and were never found. Dean warns against it, citing John's rule that you never go back to the same town. Sam doesn't believe it, and figures that Dean is trying to protecting him from breaking the mental blocks in his head. He insists that he has to make up for whatever he misses up a year ago. Dean reluctantly agrees and they split up.
Dean talks to the roommate of one of the victims, Nicole Holder, who says she was with Nicole the night she was missing. As they talk, Dean notices that she has a lot of business cards, including one for Sam's alias. The roommate confirms that Nicole got it from Sam, who was there several times. She finally admits that Nicole and Sam were having a sexual relationship.
As Sam walks down the street, the deputy finds him and places him under arrest. He locks up Sam and tells him that he confirmed with the FBI that Sam wasn't an agent, and figures that Sam is the person who killed the five men. Sam pleads amnesia but the deputy doesn't believe him and walks away. Later, a woman comes in, asks where her husband is, and says that she knows who he really is. Sam remembers talking to Sheriff Roy Dobbs and the woman, who is Dobbs' wife, and them asking what they can do. The woman explains that Dobbs was her first husband, and wants to know what happened to him. She finally accepts Sam's story that he can't remember and introduces herself as Brenna Dobbs. He asks her to let him out so he can find the answers, and she agrees.
The woman from the restaurant, Debbie Harris, is drinking and her husband Don looks on in disgust. Once he leaves, the woman goes down to get some more wine, trips, and screams as something approaches her.
Sam is at the motel when he hears someone moving outside. He draws his gun and aims it at the intruder... Dean, as he comes in. Dean tells him that he's confirmed that Sam was active with the women a year ago. They hear a police dispatch and Dean says that he'll check it out, and Sam has to stay in the motel. Sam agrees, but then leaves as soon as Dean is gone.
Dean talks to Don, and confirms that Sam was sleeping with all of the victims. He calls to warn Sam that it was a trap, and leaves a voice mail.
Sam goes to Brenna's house and asks for the sheriff's case files. She tells him to go the station, but he says he's already been there and they're gone. Sam promises to find out what happened a year ago, and stop what's happening now. Brenna agrees and goes to get the files. As she goes, Sam remembers him and his grandfather talking to Brenna and Roy, and discussing family and how they slow you down. Brenna brings back the files, and Sam remembers seeing the dead men, and Samuel saying that an arachne is responsible for the deaths. Sam then figured out they needed to lure it to them. In the present, Sam asks to take the evidence with him, and Brenna explains that she's made peace with Roy's death, and now she just wants to know what happened. Sam assures her that Roy died as a hero.
As Sam leaves, he checks his voicemail and gets Dean's message. He looks around and realizes that Brenna's house is shrouded in spider webs. He examines the webs, unaware that something is watching him from the shadows. Dean comes up behind him, and insists that Sam should have stayed behind. As he gets him out, the creature watches from the shadows.
Back at the motel, dean covers what they have, and Sam tells him that they're up against an arachne. He assures Dean that so far, he isn't remembering anything about Hell, but Dean wants to get out of town. Sam is sure that he knows who the killer is, but he can't remember. He still insists on setting things, and his soul won't let him walk away. Sam asks Dean to stay with him and back him up, and Dean reluctantly agrees. They go over all the information they've gathered, and Sam remembers shooting someone and later attacking the deputy.
A year ago, Sam calls Roy and convinces him to meet them in the park. He plans to use him as bait without telling him, ignoring Samuel's objections. The two men watch Roy in the park until a female figure, the arachne, attacks him. It escapes with Roy before they could stop it, but Sam tracked it using Roy's cell phone GPS. They follow the signal to an abandoned house and find the five missing men, wrapped in webs. The arachne arrives and knocks Sam aside, and Samuel shoots it. It's immune to bullets, but Sam recovers and manages to decapitate it. Samuel promises Roy that they can help him, but Sam warns that it's too late and the spider's poison is fatal. He says all they can do is put the men out of their misery, tells Roy that he's a hero, and then shoots him dead. After killing the others, Sam says they need to burn the bodies.
Sam tells Dean that he knows what happened.
Brenna is sleeping at home when she hears someone at the door. She goes to investigate and finds Roy, hideously disfigured, waiting for her. He says that he loves her.
Sam calls Brenna, who asks him to swing by. He realizes that he's in trouble and the brothers go to her home. They see a light on in the shed and investigate, and find Brenna cowering in a corner. She asks Sam if what he did to Roy is true. Roy grabs Dean and throws him back, and then grabs Sam and tells him to answer the question.
Roy webs the brothers up, and Sam asks him to let Brenna go. Roy points out that Sam was hanging around with Brenna, and the arachne was in town to breed. She bit them to turn them into what she was. The bullets and fire had no effect on them, and four of the five men fled. Roy remained in town and plotted his revenge against Sam. He tells Sam that he transformed the missing women into arachne and they've fled the town. Now Roy wonders whether to kill Sam or turn him. Dean manages to cut himself loose with a piece of glass and attacks Roy, but Roy easily overpowers him. Brenna tries to stop her husband, but he ignores her. She cuts Sam free, and he decapitates Roy.
Sam takes Brenna home and tries to apologizes, but she goes inside without a word and closes the door behind her.
At the motel, Sam admits that Dean was right and they shouldn't have come back. Dean tries to reassure him that his soulless self wasn't Sam, but Sam doesn't believe it. He wonders what else he's done, and then collapses to the ground, convulsing. He remembers himself on fire, burning in Hell.