On March 15, 1937, in Providence, Rhode Island, writer H.P. Lovecraft is drinking heavily and finishing a new manuscript when the study door creeks open. He calls out but gets no answer. Drawing a gun, Lovecraft goes to the door and looks outside, but sees nothing. He locks the door but a figure smashes through the window and advances on him. Lovecraft says that they didn't know, but the intruder kills him.
At Bobby's house, Dean and Sam are going over their grandfather's journals without success. Bobby tells them that they're missing a critical journal, and Castiel stole it when he visited the previous night. Fortunately, Bobby kept a copy. There are references to something that occurred on March 10, 1937, and Lovecraft wrote about portals to dimensions. Bobby figures that Lovecraft knew something about Purgatory since Moishe paid him a visit.
Ben is in his room reading while downstairs, Lisa watches baseball with her new boyfriend, Matt. Demons break into the house, kill Matt, and take Lisa captive. Ben sees them and runs to his room, locking the door behind him. He calls Dean who tells him to jump out the window while he comes to get them. Ben drops the phone and Dean tries to get through to him, and Crowley picks up the phone. He tells Dean that he's holding Ben and Lisa hostage to force Dean and Sam to stand down.
Dean tells Bobby and Sam what's happened, and starts to leave. Sam insists on going with him and Bobby reluctantly agrees to keep pursuing the Lovecraft angle. As he leaves, Sam and Dean summon Balthazar and ask for his help finding Lisa and Ben. He's surprised when they tell him that Castiel and Crowley are working together and splitting up the souls in Purgatory. However, Balthazar refuses to help them and teleports away. Sam suggests that they call Castiel, but Dean refuses.
Posing as a journalist, Bobby meets with a Lovecraft collector and asks if he has any letters concerning Lovecraft's last years in March, 1937. The collector notes that another "journalist" has already been there, and Bobby realizes from the description that it's Castiel. The Lovecraft fan tells Bobby that Lovecraft had a party on March 10, 1937, and the guests were co-worshippers in a black magic cult. They were going to open a portal to another dimension but apparently failed. The collector discovers that all of the correspondence has disappeared. Bobby realizes that Castiel has stolen them and quickly departs. He calls Sam and tells him what he's discovered, and notes that all of the guests died or disappeared within a year. Bobby is going to see the maid's son, who is now 83 years old and locked in a mental ward since 1937.
Dean is busy torturing demons for information on Crowley, and has one tied up and caught in a Devil's Trap. Sam comes in and warns him that he's on the thin edge of exhaustion, but Dean figures that eventually he'll convince a demon to talk and he doesn't want Sam to interfere.
Sam steps outside and prays to Castiel to bring Lisa and Ben back. He gets no response, but is unaware that an invisible Castiel is watching him. Castiel goes to see Crowley, who readily admits he took Ben and Lisa as a way to bypass Castiel's order not to harm Sam and Dean. Crowley refuses to tell the angel where his captives are, and tells Castiel to find Purgatory so they can put things to an end. Before he can respond, Castiel receives a summons from Balthazar. He goes to see his friend, who asks if he's working with Crowley. Castiel denies it but Balthazar points out that he's a terrible liar. When Castiel explains that he plans to suck up all the souls to win the war in Heaven, Balthazar notes that if he miscalculates, the power could destroy most of Earth. Castiel apologizes for not telling him the truth and asks Balthazar if he's with him. After a few moments, Balthazar says that he'll support him in his bid for power. He then admits that he learned about Castiel's plan from the Winchesters.
Bobby talks to the maid's son, who tells him that Castiel already talked to him. The man asks if Bobby believes in monsters, and warns that if he does, they'll lock him up. Bobby assures him that he'll accept whatever he says, and the old man says that the spell worked and an invisible creature came through. It possessed his mother, who disappeared without a trace. A few days later, the guests were killed. Bobby offers his condolences and the old man admits that he's the first one to ever do so. He gives Bobby a photo of his mother, Eleanor, and Bobby stares at it in shock.
Dean prepares to torture the demon but unwittingly smears the Devil's Trap as he crosses over it. The demon breaks free and telekinetically shoves Dean back, frees himself, and then advances and starts throttling him. Castiel arrives and smites the demon, destroying it. The angel says that he had no idea Crowley was going to take Ben and Lisa, but Dean doesn't believe anything he says. Castiel says that he's always come through and is Dean's friend, and asks Dean to trust him. He promises to find Lisa and Ben, and asks Dean to stand behind him this one time. Dean points out that Castiel is asking him to stand down in return for Lisa and Ben, and tells Castiel that he'll find them on his own. Castiel departs without a word.
Bobby drives to an isolated cabin with a warding sign on the door. Dr. Eleanor Visyak answers the door and invites him inside. Her former lover admits that he knows all of her safehouses and knows that she's Eleanor, the maid in 1937. He shows her the photo the old man gave him, and points out that she fibbed about her age, which is 900 years. Visyak explains that she's nothing like Eve, and fell through by accident. She likes Earth and doesn't want to see it destroyed. Visyak has spent the last 75 years trying to keep Purgatory closed, and gave Dean the sword so they would stop dragons. Bobby warns that Castiel is on her trail and will eventually tack him down, and he wants to know the ritual to open the door. Visyak refuses, saying that the secret is safe with her and Bobby can't protect her.
Sam returns to Bobby's house and pours himself a drink. Balthazar teleports in and says that he has no choice but to join up with them. When Dean comes in, Balthazar explains that he's not convinced that Castiel can handle the power of the Purgatory souls. He has already found Ben and Lisa and agrees to teleport the Winchesters there. However, the building is warded against angels so he can't enter. Balthazar takes them there and then quickly leaves. The brothers take out the demons guarding the perimeter and split up to search for Ben and Lisa. Sam is soon knocked out and locked in a room.
Dean fights his way into the room where Lisa and Ben are tied up. He unties them and gets them moving to the door, but Lisa pulls out a knife and threatens Ben, revealing that a demon has possessed her. The demon taunts Dean and Ben, saying that it knows Lisa's thoughts. First it claims that Dean is Ben's real father, but then says that Lisa was a slut and has no idea who Ben's father was. The demon then tells Dean that Lisa considers him the second-worst mistake she ever made, and keeping Ben was her first-worst mistake. Dean throws holy water into the demon's face, kicks the knife away, and starts performing a ritual of exorcism. As it starts to take effect, the demon stabs Lisa's body in the stomach. If Dean completes the ritual, the demon will be exorcised and Lisa will die. Dean finishes the ritual and then runs to Lisa as she collapses. He tries to call Sam without success, and then has Ben grab a shotgun and cover their escape while he carries Lisa out. Ben shoots down a demon and they find and free Sam. Outside, Sam hotwires a car and they drive to the hospital.
At the hospital, Ben and Dean stand watch over the mortally wounded Lisa. Dean tries to apologize to the boy, who angrily leaves. Castiel arrives and tries to apologize, but Dean isn't interested. The angel heals Lisa and Dean thanks him. However, he says that it doesn't change anything between them. As Castiel goes, Dean asks him to do one more thing.
When Lisa wakes up, she finds Ben at her side. He tells her that they were in a car accident. Dean comes in and claims that he was the driver who hit them, and they have no memory of who he really is due to Castiel. He says that he's glad that they're okay and they can go back to their normal lives, and Lisa says that the important thing is that they're all right.
As Dean leaves, Sam complains that he's tampering with their minds. Dean tells him never to mention Lisa and Ben again or he'll break Sam's nose. Sam stays quiet and they drive away in the Impala.
As Visyak leaves her cabin, Castiel teleports behind her, grabs her, and teleports away with her.