During a raid on Richard Roman Enterprises, Sam and Dean Winchester manage to get a block of clay that Dick Roman was after with the help of Charlie Bradbury. That night, they break open the clay to reveal a tablet that they can't read. At the same time, Castiel is awakened from his catatonia and Kevin Tran becomes a Prophet and is compelled to steal his mom's car and drive somewhere. After hearing from Meg that Castiel is awake, the Winchesters travel to Northern Indiana State Hospital in hopes that Castiel will have some answers.
Reaching the hospital, Sam and Dean find that Castiel has gone insane from absorbing Sam's Hell madness to save him. Castiel explains that he woke up when he heard a ping that only angels can hear. When Sam shows him the tablet, he explains that it is the Word of God and was written by the Scribe of God Metatron who took it down when Creation was being formed. However, he doesn't know what it says as angels can't read it. As Dean argues with Meg about her being allowed to look at it, Castiel declares he doesn't like conflict, drops the tablet which breaks into three pieces and teleports away. After Meg tells Dean Castiel is likely in the dayroom, Sam stays with Meg to pick up the pieces of the tablet.
After Sam and Meg leave the room due to an argument when Sam won't tell her what's going on, they return after hearing a noise to find the bag containing the tablet gone, having been stolen by Kevin. Meg and Sam chase down Kevin with Meg eventually taking him down. Meg is surprised as he's human, but Kevin is unable to let go of the tablet for some reason. Returning to Castiel's room, Kevin tells them that all he knows is he's supposed to keep the tablet even though he doesn't know what it is. When Sam tells him to open the bag, Kevin pulls out the pieces and shocks Sam and Meg by being able to repair the tablet just by putting the pieces back together. Afterwards, Kevin discovers he can read the tablet and asks Sam what Leviathan is. Kevin explains that the tablet is difficult to read, but it talks about how the Leviathans came to be and how God locked them up far away. Sam asks if the tablet shows a way to kill the Leviathan, but Kevin informs him that its hard to focus on for too long and read it.
At the same time, Dean finds Castiel and tries to get answers from him, realizing that it was what he took from Sam that drove him insane. However, Castiel is more interested in playing Sorry! then giving Dean answers despite his best efforts. Dean asks about where he can find Metatron, hoping he can help them find some answers, but Castiel tells him the universe is engineered to create conflict and he doesn't make the rules. Dean reminds him of when he became God and made the rules, but Castiel just apologizes to Dean's frustration. However, Castiel senses that Sam is talking to angels and returns to his room.
Moments after Kevin discovers he can read the tablet and it talks about the Leviathans, Meg senses something and two angels, Hester and Inias appear and Hester sends Meg flying. Hester is angry to find a Winchester with a demon once again and calling Kevin a Prophet announces that they are there to take him. Hester orders Inias to kill Sam and Meg, but Meg pulls an angel blade to Hester's shock and slices open Inias' palm. Before anymore can happen, Castiel teleports in to the other angels' shock as they believed him to be dead. Hester angrily demands answers from Castiel for his actions and quickly realizes he's insane from his response. Before things can degenerate anymore, Dean catches Hester's attention and then banishes all three angels. Sam then questions Meg on where she got an angel blade and she tells him that "a lot of angels died this year."
The Winchesters explain the situation to a stunned Kevin who reveals that the tablet acts as a kind of "in case of emergency" note, making them realize that it may hold a way to defeat the Leviathans once and for all. Dean is surprised to hear that Hester told Kevin he was a Prophet, but Meg tells them they need to leave before the angels come back and that she's coming with them for safety in numbers. Dean reluctantly lets Meg come along and they decide to head for Rufus's Cabin where Kevin can translate the tablet for them to see if it has a way to stop the Leviathans.
Along the way to the cabin, the Winchesters and Meg stop for supplies at a minimart and Sam sees a report stating that Kevin is believed to have been kidnapped while Meg spots two demons, Rosco and a friend of his nearby. As they continue their trip, Meg gets a call from Castiel who ultimately ended up at a dog track in Perth, Australia. After Meg gives him their location, Castiel teleports into the car with them. Castiel explains the angels are from his old garrison which Hester must've taken command of and that they are following protocol which states that when the Word of God in unearthed and the Keeper of the Word is awakened, the angels must take the Keeper to the desert to learn the Word away from men. Dean is annoyed as they need Kevin to translate the Word so that they can stop Dick Roman and his plans so Castiel warns him that they will have to duck Hester and her soldiers and that he doesn't fight anymore in his new state so he won't be any help to them if it comes down to it.
Arriving at the cabin, Sam and Castiel put up angel warding, but don't angel proof the cabin as Castiel would be expelled from the cabin by the warding. Afterwards, the two discuss the burden Castiel lifted from Sam's mind and Castiel informs him that while he doesn't see Lucifer, he now sees "everything." Castiel explains that before he took on Sam's madness, the weight of all of his mistakes, all the lives and souls lost because of him was too much for him but when he took on Sam's pain, it helped him start to deal with it. At the same time, Dean takes Kevin into the basement to translate the tablet, but Kevin starts hyperventilating over the pressure and the changes his new status as a Prophet has caused to his life. Dean helps him through it, telling him it sucks, but the angels don't care and Dean doesn't think they can, saying that when they try to care, it just breaks them apart. Calming down, Kevin eventually goes back to work.
Leaving the cabin, Meg meets up with Rosco and the other demon on the road, having arranged to meet with them before leaving the gas station. When asked why the demons shouldn't just turn her over to Crowley, Meg tells them that she's got Castiel and can give him to them. Before she takes the demons to Castiel, she asks how many demons she will have to cut in on the deal. Rosco tells her they aren't stupid and didn't tell anyone. Commenting "I love demons," Meg quickly kills the second demon with the demon-killing knife and engages Rosco, ultimately defeating and killing him.
Meg returns to the cabin where the Winchesters have noticed her disappearance and that of the knife and have prepared a devil's trap to catch her when she returns. After turning over the knife, Meg is annoyed that she just saved them from two demons and comes back to a devil's trap, pointing out she could've easily betrayed them to Crowley instead. Castiel backs up her claim by telling the Winchesters that there is the blood of other demons on the knife. Meg explains that what she does is pick a cause and commit herself to it. In the past it was Lucifer and Azazel's cause, but now its killing Crowley. When Dean points out that Crowley is not the enemy currently, Meg tells them that Crowley is always the problem and is just waiting for the right moment to strike. As she knows she needs help to stop him, Meg has no intention of betraying the Winchesters or Castiel, the only humans and angel she can trust to help her. Believing Meg's story, Sam breaks the devil's trap and frees her only to have Castiel warn them that Meg killing the demons put out a beacon to the garrison where they are and Hester will be coming.
Before they can put up better angel-proofing, Hester returns with Inias and another angel. Hester furiously confronts Castiel over helping keep Kevin from them while Inias pleads with Castiel to help them do their work. After Dean tells him that Castiel can't help anybody, Hester tells them that they don't need Castiel's help or permission and has Inias retrieve Kevin. Dean asks the angels to give them time to have Kevin translate the tablet so that they can defeat the Leviathans and clean up Castiel's mess. Angrily declaring that Dean has corrupted Castiel and that he's going to pay, Hester goes to attack Dean only to have Castiel block her and point out that the angels are supposed to protect the humans. Hester punches Castiel and as Inias and the other angel hold Sam and Dean back, beats on Castiel who doesn't resist, venting her anger at him for his actions. As Hester prepares to kill Castiel with her angel blade, Inias tries to get her to stop as there are so few angels left, but Hester is beyond reason, punching Inias and then preparing to stab Castiel, stating that "you wanted free will? Now I'm making the choices!" As Hester goes to kill Castiel, Meg stabs her through the back with her angel blade, killing Hester. Meg tells everyone that someone had to do it as Hester was out of control.
With Hester dead, Inias takes command and reaches a truce with the Winchesters where he allows Kevin to complete the translation before taking him away. Meg departs and Castiel believes she is laying low again following the events. Though Inias offers Castiel the chance to return to Heaven with them, Castiel declines, telling Inias that he's not part of the garrison anymore. After Kevin has finished translating the tablet, he gives the translations to the Winchesters and departs carrying the tablet with two angels as his escort who are ordered to take him home and watch over him there rather than going to the desert as the angels had originally planned. Reading Kevin's translations, Sam discovers a way to kill a Leviathan: the Bone of Righteous Mortal Washed in the Three Bloods of Fallen. The translation lists Fallen Angel's blood as the first ingredient so Castiel, now considered a Fallen Angel, happily gives the Winchesters a vial of his blood before departing for an parts unknown, even to him.
The angels return Kevin to his mother who has been searching for him and is waiting for news with Detective Stein. Kevin and his mother are tearfully reunited, but after Kevin reveals that the angels are there to protect him, the detective comments he doesn't think that's true. The detective quickly reveals himself to be a Leviathan and easily kills the two angels with their powers having no effect on him. The detective then turns back into the Leviathan Edgar, having been sent by Dick Roman to find Kevin as soon as he was made a Prophet. With Kevin's protectors dead, Edgar kidnaps Kevin and his mother and takes them to Dick at SucroCorp.
Now knowing how to kill a Leviathan, the Winchesters set out to gather the remaining ingredients for the weapon and use it against Dick.
Following his kidnapping, Kevin is forced to translate the Leviathan tablet for Dick Roman in exchange for his mother's freedom. Knowing what the Winchesters need for the weapon, Dick sends Edgar to kill the Alpha Vampire and summons Crowley to make a deal, but the Winchesters defeat Edgar and Crowley betrays him and gives the Winchesters the right blood.
The Winchesters, Castiel and Meg eventually use the information they learned from Kevin's translation of the Leviathan tablet to attack SucroCorp and kill Dick Roman, effectively defeating the Leviathans. During the battle, Sam rescues Kevin, but Crowley kidnaps him for his own purposes after Dick is dead. He later escapes, but as a result of the angels sent to protect him being so easily killed by Edgar, Linda Tran refused further angelic protection afterwards.
- The Word of God tablets are introduced, an important plot point in seasons 8, 9 and 13 with the demon and angel tablets. Kevin Tran also becomes a major recurring character until his death at the hands of Gadreel.
- Meg is caught in a devil's trap for the third and last time on the show, making her the demon caught the second most times after Crowley. Notably, she is released this time by Sam rather than being exorcised or escaping like the last two times. She also states that her cause in life is now to kill Crowley which she is shown to be so dedicated to, that she doesn't care if she gets trapped in Hell when the Winchesters close the Gates of Hell as long as Crowley is dead.
- Meg, a demon, kills Hester, an angel. This is the first time a demon has killed an angel on the show and is a feat only repeated twice on-screen by Crowley.