At a Nazi base in Witsyebsk, Belarus, a huge figure of a man launches a one-man attack on the Nazi guards. The alarm goes off and inside, Commander Eckhart finishes writing down the results of his experiments into a ledger. He tells his men to guard the door and they prepare to open fire. When the intruder storms in, they open fire but their bullets are useless. As the intruder kills them, Eckhart finishes casting a spell and tells the attacker to inform its masters that it isn't over between them. he then disappears in a burst of flame, the fire spreading to destroy the compound.
Sam and Dean drive to the coordinates that Larry gave them near Lebanon, KS. They find an abandoned dam at the coordinates and use the key to go inside. They discover that the Men of Letters created a vast underground base within the dam and that it has been untouched since the 1950s when the Letters abandoned it on short notice. Dean is happy to notice that the Letters lived in and takes a hot shower, while Sam goes through the group's extensive research library.
In Wilkes-Barre, PA, Rabbi Isaac Bass goes to the college library to continue his research into the materials left to the college by the Holtzinger Estate. Bass finds a ledger in a case and studies the writing with interest, and then runs to the librarian and tells him that they have to protect the book. He tells the librarian that a man is following him and wants the book, and the librarian assures him that the collection will be safe.
As Bass leaves, a man named Torvald follow shim to a local bar. Inside, bass makes a call and leaves a message for someone named Aaron, reading off a number. Once the rabbi finishes the call, he goes to the window and shouts out at Torvald, inviting him to come in for a drink. While the patrons wonders what Bass is doing, the rabbi suddenly bursts into flames.
Two Weeks Later
After checking with Kevin and Garth, Dean tells Sam that he hasn't had any luck summoning Castiel with prayer. Sam explains that he's been performing research on the Letters and discovered that they had one faction, the Judah Initiative, which worked in Europe and fought the Nazis. The last surviving member, Isaac Bass, died in Wilkes-Barre two weeks ago of spontaneous combustion and the brothers figure that they have a case.
When the Winchesters arrive in Wilkes-Barre, Sam talks to the librarian, claiming that he was Bass' partner. Meanwhile, Dean goes to the bar and talks to two women, Sharon and Ariel. They confirm they were there the night that Bass died and that he was always ranting and raving about Nazis. A young man at the bar, Aaron, looks suggestively at Dean, while the women tell Dean that the fire consumed Bass as if it were alive.
At the library, Sam opens the case that Bass was examining and discovers that it contains a book on birdwatching.
Dean goes over to the man, Aaron, and asks why he's been following him since earlier. Aaron flirts with him and claims that he just followed Dean to get a date. Dean backs off and goes outside, and Sam calls to tell him what he found. As Sam talks, he sees someone following him and tells his brother, and they agree to meet at the visitor's parking lot that night and Sam's follower. When they meet there, Dean sneaks up on the man, a huge figure who casually throws Dean through the air. Sam attacks the man with the demon-killing knife but it simply ignores the wound, which doesn't bleed, and starts choking Sam. Aaron finally arrives and tells the huge man to stop, and explains that he's a golem.
The trio take the golem to Aaron's apartment and Aaron explains that he's Bass' grandson. His grandfather sent the golem to him, explaining that it is shaped from clay and brought to life by rabbis to protect the Jewish people. When Aaron learned about Isaac's death, he came there to investigate, aware that his grandfather was a member of the Judah Initiative. When the Winchesters admit that they know about the organization, the golem speaks up, asking why they should know about it. The brothers confirm that they know about the Men of Letters and the golem accepts them for what they claim. As they talk, they're unaware that Torvald is outside watching them.
The brothers explain their family connection to the Hunters and the Letters, and Aaron admits that he has never been involved with the supernatural. He figured that his grandfather was just making up fantasies to avoid looking too hard at his past in the concentration camps during World War II. As they talk, the golem paces unceasingly around the room and complains about how Aaron doesn't follow Jewish tradition. When Aaron tells it to shut up, the golem says that he has to take charge and then goes back to pacing the room. Aaron then explains that Isaac was tracking down a group of Nazi necromancers known as the Thule Society. The golem tells Aaron to find the Thules so that he can do his work, and Aaron informs the Winchesters that Isaac left him a number on his answering machine on the day of his death. When he recites the number, Sam realizes that it's a library call number and figures that it's connected to the birdwatching book that he found at the library.
The group goes to the library and breaks in, and Sam goes to the indicated section to find the book. He discovers it in the slot where the birdwatching book was, where Isaac swapped books, but Torvald shoots him with a dart. Sam starts to collapse as the magic on the dart starts to kill him, but manages to kick a cart into Torvald and runs to the stairs. As he collapses, Torvald shoots Aaron with another dart. Dean tells the golem that Aaron will die if they don't find Torvald, and the golem stomps upstairs and manages to grab Torvald. He knocks the necromancer out and drags him downstairs. Torvald vows that the Thules will live forever and the golem breaks his neck, ending the spell and saving Sam and Aaron.
Aaron wakes up later after the brothers drive out into the countryside to burn and bury Torvald's body. The golem tells Aaron that the Winchesters saved his life. At the grave, Dean tells Sam how the golem brutally killed Torvadt and they wonder if they should destroy it. Meanwhile, Aaron watches the brothers burn the corpse and figures that they're psychopaths.
The next day, the trio goes back to Aaron's apartment and reads the recovered book. Aaron realizes that it's the Red Ledger, which documented the Nazi experiments at Witsyebsk. The golem speaks up, explaining that it was there at Witsyebsk, and Sam realizes that it attacked the camp. It tells them that Eckhart destroyed the camp with a flame spell and then tells Aaron to take charge. When Sam asks why it keeps saying that, the golem says that Aaron should know what to do by consulting the pages. Aaron admits that he had the book, which Isaac gave him, but he used the pages to roll cigarettes when he was in high school. When Aaron asks the golem to tell him how to control it, the golem angrily says that it's not his place to teach the teacher.
Sam continues reading the Red Ledger and discovers that the Nazis were experimenting on their prisoners, killing them and attempting to resurrect them. Once they perfected the resurrection process, they used it on themselves. According to the entries, a reanimated body can be killed with a head shot but will come back to life in twelve hours if it isn't burned.
The young Eckhart arrives at the library and goes in with his assistant. They examine the area where the golem attacked Torvald and Eckhart confirms that the Winchesters eradicated Torvadt's spirit so that he can't interrogate it. When Eckhart checks the shelving, he finds bits of clay and realizes what killed Torvadt.
Dean calls Garth to have him check on the Thules but there's nothing in the records about them. Sam has checked on ways to destroy a golem but can't find anything specific. Some legends refer to the word "truth" inscribed on its forehead, while others talk about a scroll in its mouth. Aaron overhears them talking and realizes that they plan to destroy the golem, but insists that it's his responsibility to deal with it. However, Dean points out that he can't control it and Aaron admits that he doesn't know how.
Eckhart and his men break into the house and quickly capture them. The golem fights back, killing one of them, but Eckhart takes control of it with a spell and then orders it to give him the controlling scroll in its mouth. Once Eckhart has it, he wonders why Aaron didn't control the golem and explains that all he had to do was write his name on the scroll. The Nazi has his men search for the Red Ledger, unaware that Sam has dropped it at his side. Meanwhile, Dean gestures for Aaron to pick up a discarded shotgun, but Aaron refuses.
The Thules finally locate the Red Ledger and Eckhart thumbs through it to make sure everything is safe. Aaron finally has enough and hits Eckhart over the head. Sam and Dean grab their guns and shoot two of the three remaining Thule soldiers, while the last one ducks behind Aaron and escapes. Unimpressed, Eckhart tells them to kill him but that the Thule Society will live on. The Winchesters oblige and then make sure that Aaron is okay.
After disposing of Eckhart's body, the three men return to Aaron's house and the Winchesters ask Aaron if he wants them to get rid of the golem. Aaron says that the battle against the Thule Society isn't over and his grandfather left him something important to do. He writes his name on the scroll and then puts it in the golem's mouth, and it nods to him in a gesture of obedience. Aaron tells the Winchesters that the Judah Initiative is reborn.
When they return to the Letters' headquarters, Sam begins transcribing the Red Ledger. Dean asks his brother if he's going to become a Man of Letters and says that it's good if he is.