After learning of the state of Heaven, the angel and former Scribe of God Metatron expels all angels from Heaven in a form of revenge. After being alone in Heaven, Metatron decides that he wants to let only the angels he wants back in under his command so he won't be lonely and recruits Gadreel as his second-in-command. After killing the Prophet Kevin Tran, Gadreel stole the angel and demon tablets and brought them to Metatron who used the power of the angel tablet to give himself God-like abilities. Wanting to write an epic "story" with himself as the hero, Metatron used an illusion of Gabriel to try to get Castiel to build an army against him and be his story's villain. While Castiel initially refused, the sheer power Metatron possessed now due to the angel tablet caused him to change his mind and use the Horn of Gabriel to start organizing angels against Metatron who had Gadreel use the same sigil to gather angels to his own side.
Castiel proved to be an effective leader, gathering a massive following that outnumbered Metatron's own followers. There were also angel factions who were unaffiliated while Metatron had Gadreel kill major faction leader Malachi when he refused to join with him. After Castiel's faction captures Metatron loyalist Ezra, they learn that Metatron has an elite ground force and a portal to Heaven that he alone controls before Josiah assassinates him with an angel blade and then flees. Unknown to the Winchesters and Castiel, this elite force were brainwashed angels who were apart of Castiel's army and made to become suicide bombers in the name of Castiel to turn the angels against Castiel.
Starting his suicide bombings, Metatron sends Oren to an ice cream parlor in Dixon, Missouri where one of his loyal angels, Esther is having ice cream in the form of a little girl. Spotting Oren, Esther tries to warn the humans to run, but Oren reveals a sigil carved into his chest and pulls an angel blade. Proclaiming that "I do this for Castiel," Oren stabs himself in the sigil when near Esther, atomizing his fellow angel and releasing a massive blast of grace that kills six other humans in the ice cream parlor in a fashion similar to smiting.
After learning that something is going down in Missouri, Dean wakes Sam and they take off to meet up with Castiel. While Sam insists Dean leave the First Blade behind, he only pretends to and secretly takes the weapon with him. Castiel shows them the body of one of the humans and tells them that he hasn't ever seen anything like it and believes it to be an attack directed against him by Metatron.
In Heaven, Gadreel expresses concern about the state of things, notably that Castiel's army outnumbers their own and how Metatron had a meeting between Gadreel and Castiel attacked, nearly resulting in both of their deaths. Metatron tells Gadreel he gave orders that Gadreel was not to be harmed and Gadreel insists that while he did meet with Castiel, he didn't believe what he was told. Metatron tells Gadreel that while he wanted Castiel to lead an army against him, he didn't think Castiel would actually be good at it. Metatron reassures Gadreel that he has a plan on how to make a good impression at their later meeting with Tyrus, the leader of the largest independent faction of angels left.
Returning to Castiel's base, they are informed by the angel Hannah of the disappearance of Josiah shortly after Ezra's murder and believing Josiah to be the killer and Metatron's spy in their ranks, Sam begins a search for Josiah using his vessel's credit card. Shortly after Sam finds something, an angel who was examining the evidence from the ice cream parlor finds a video on someone's cell phone of Oren's attack. The angels and the Winchesters learn of how Oren blew himself up in Castiel's name and Castiel insists upon his innocence, saying that he would never ask an angel to kill themselves in such a fashion and murder innocents. Hannah recognizes Esther as one of Metatron's angels from the video, but Castiel insists he doesn't know why an angel would do such a thing in his name. Dean is suspisous as the last time Castiel had an army and was at war, he committed terrible acts and lied to both him and Sam about it the whole time. Sam has them take the discussion to Castiel's office so that its private and asks Castiel about Oren. Castiel explains that Oren was a new recruit who worked in community outreach by working with some other angels at a local hospital and causing minor miracles that wouldn't draw attention. Castiel tells them that he believes that the sigil carved on Oren's chest focuses energy and when Oren stabbed himself, it unleashed all of the focused power. As Esther was in the path of the blast, she was likely atomized by it. Dean decides to talk to angels who knew Oren and tells Castiel to stay out of it, believing the angels won't say anything with Castiel there. Castiel reluctantly agrees and decides to follow Josiah's trail to Colorado with Sam instead.
Learning that Oren worked with an angel named Flagstaff at the hospital, Dean interrogates her for information on Oren's activities. Flagstaff tells Dean she doesn't know why Oren would kill himself in such a manner and that she despises Dean for his belief that he can save lives through violence but actually has "oceans of blood" on his hands while she saves lives with minor miracles. Enraged, Dean attacks Flagstaff and holds an angel blade to her throat. Dean demands the names of any friends of Oren's from a panicked Flagstaff who tells him that Constantine and Tessa were his friends. Dean is shocked by the second name and asks if she means Tessa the Reaper which Flagstaff confirms.
Having learned of Tessa's connection to Oren, Dean begins searching for her, but finds her missing from the hospital and that so is an ambulance. As the ambulance has a GPS, Dean is able to use it to track Tessa to an theater where he confronts her. Tessa refuses to talk to Dean and tries to leave, but Dean grabs her by the arm, causing her jacket to come down a bit and exposing the same sigil that Oren used. Realizing that Tessa is another suicide bomber, Dean quickly captures her with the binding handcuffs and demands to know where Constantine is. Tessa refuses to cooperate so Dean uses an angel blade to destroy the sigil Tessa carved into her chest to "defuse" her in case she finds a way to escape. He then takes her back to Castiel's base for interrogation.
Metatron and Gadreel meet with Tyrus in a bowling alley to get him and his angel faction to join them. However, Tyrus is not interested as he and his angels like it on Earth as he likes the authenticity of things here, he likes being an independent operator, he knows Metatron is losing the war and he hates Metatron himself, seeing him as "a nerd trying to be one of the popular kids." Metatron has Gadreel draw an angel blade to force Tyrus to cooperate, but Tyrus is unthreatened as if Metatron kills him, Tyrus' faction will simply join with Castiel and he knows Metatron is not that stupid. Instead, he offers to hear Metatron out if Metatron can out-bowl him which Metatron accepts. Metatron ultimately loses the round, but as he and Gadreel start to leave, Constantine arrives and blows himself up in Castiel's name, killing Tyrus and injuring Gadreel who shields Metatron.
As he returns to Castiel's base, Dean calls Sam to let him and Castiel know of Tessa's capture while Flagstaff angrily tells the other angels of Dean's actions towards her. Dean arrives with the captive Tessa, shocking Hannah when she sees Tessa captive and the damage Dean did to her to defuse the sigil. When Hannah exclaims "oh god", Tessa tells her that "there is no God. There is only Castiel." Dean locks Tessa in the base's cell and informs the other angels he intends to torture Tessa for information as they need to know if there are any other suicide bombers out there. However, Hannah refuses to let him do it, telling him that only Castiel can punish Tessa for her actions. Hannah explains that a month before, half the angels in the army were trying to kill the other half but Castiel has given them rules and order. If she allows Dean to take matters into his own hands and torture Tessa, there's nothing to stop another angel from doing the same. Hannah agrees to let Dean talk to Tessa, saying that he should do that, but won't condone torture and demands Dean turn over his angel blade before entering the room. When the angels make it clear that they won't allow him in any other way, Dean turns over his angel blade before entering Tessa's cell.
Hannah and Dean question Tessa who tells them that she is following Castiel's orders. Tessa explains that the suicide bombers are targeting Metatron's followers and feel that sacrifices have to be made to win the war. She tells Hannah and Dean that Castiel had come to her with this mission as he felt she was strong enough for it and that others, such as Hannah, were not. Hannah tries to attack Tessa for her words, but Dean restrains her and pulls her from the room. Dean tells Hannah that while he's not sure if Tessa is telling the truth about Castiel being behind the suicide bombings, Tessa believes she is. As Hannah can't handle the implication that Castiel might be behind the suicide bombings, Dean has her wait outside while he questions Tessa by himself. Dean uses their past to try to get Tessa to explain everything to him, asking why, beyond Castiel, she'd be willing to kill herself in such a manner. Tessa explains that as a Reaper, she can hear all the souls trapped in the Veil, unable to get into Heaven due to Metatron sealing it off. Tessa's job is to transport the souls to Heaven and her inability to do her job and help them has driven her into a depression and made her suicidal as she saw death as a better option than having to suffer. While she could've taken her own life before, she didn't have a reason to until Castiel gave her a reason with the suicide bombings. Dean tells her that that's not like the Castiel he knows, but Tessa points out how the Castiel that he knows wouldn't raise an army without telling Dean either. Tessa informs Dean that there are many more suicide bombers out there like her, but refuses to give up any names. In order to force her to tell him what he wants to know, Dean pulls out the First Blade to torture her. Tessa is shocked Dean has that weapon and asks what he did. When Dean tells her he did what he had to, Tessa tells him "welcome to the club" before purposefully impaling herself on the First Blade. Thanking Dean, Tessa pulls herself further onto the First Blade, killing herself. As Dean had defused her sigil, Tessa only harms herself, but it leaves Dean looking like he murdered Tessa to the other angels who subdue Dean and tie him up.
When Sam and Castiel return from chasing Josiah to a location in Pray, Montana where they had found a fake door to Heaven, they release Dean who tells them that Tessa killed herself and he doesn't know why she did it as Tessa was saying all sorts of stuff before she did it. Sam is angry as Dean had promised to leave the First Blade at home, but Dean is unrepentant in his actions despite the fact that if he had done as Sam asked, Tessa would've been unable to kill herself and without her, they have no source of information on any future bombings. Dean insists that he didn't want Tessa to die, but Sam accuses him of wanting it and pulling out the First Blade so that he could kill her. Before the argument can go any further, Hannah informs Castiel that he has a call from Metatron.
Entering the command room, they find Metatron on a video call from his office in Heaven. Metatron tells them that he called to inform Castiel that his suicide bomber failed to kill him. Metatron tells them that Constantine's attack left Tyrus dead and Gadreel wounded and Tyrus' followers, believing that Castiel sent Constantine, have now joined with Metatron. Castiel insists that Metatron is lying and points out how Metatron's own lies led to the Fall, but Metatron tells him that he did what he had to do and always does what he has to do to make the angels stronger as a family. Sam points out all the angels Metatron had Gadreel murder, but Metatron claims that the near-death experience with the suicide bomber changed him and he is now offering amnesty to all angels and they can return home as long as they serve him. When Hannah asks him why they would follow Metatron, Metatron tells her that their need to follow Castiel shows that they need to follow someone. Metatron tells them that Castiel sending his followers out to die as suicide bombers and the fact that his stolen grace is burning out and will soon take him with it is a sign that he's desperate to win the war and will do anything to win. Metatron tells the angels that Castiel only cares about himself and the Winchesters and not his fellow angels so while Metatron isn't the best leader, he's the best they got. Metatron reminds the angels that they have to make a choice and tells them to make a good one and join him before cutting the connection.
Castiel insists to his angels that Metatron was lying, but is forced to admit he was right about Castiel's stolen grace though Castiel insists that Metatron was still lying about everything else. Hannah tells Castiel that she wants to believe him, but needs proof and demands that he kill Dean as that proof. Hannah tells Castiel that Dean murdered Tessa so killing him would be punishing him for that murder. Hannah sees Dean's death as justice for Tessa's "murder" in accordance with the rules Castiel established for his followers and tells him not to lose their trust over one man. Castiel struggles with his decision, but ultimately can't bring himself to kill his best friend. Seeing this as proof that Metatron was right about Castiel only caring about the Winchesters and himself, Hannah and the other angels leave Castiel to join with Metatron, leaving him without an army to battle Metatron and only Sam and Dean left on his side.
Metatron receives word that Castiel's army is now joining him and is overjoyed while Gadreel is disquieted and confronts Metatron over his actions. Gadreel is unhappy as he recruited Tessa and Constantine for their elite ground unit and Metatron brainwashed them and sent them to blow themselves up without ever telling Gadreel his true plan for them. Metatron explains that its an old writer's trick known as "flipping the script": he built up an unbeatable enemy in the form of Castiel with Metatron as the underdog and then he made Castiel appear greedy with the suicide bombers and made a rousing speech which revealed that Castiel's weakness, that he is in love with humanity, causing his followers to see Metatron as the better option and join him. When Gadreel asks about Metatron killing Josiah, Metatron explains that Josiah was a loose end and that he was trying to use him to lure Castiel into a trap and is disappointed by the fact that Castiel didn't fall for it. Metatron tells Gadreel that when he plays against his opponents, he always makes sure he wins.
The Winchesters and Castiel return to the Men of Letters bunker where Sam is angry about Dean lying about taking the First Blade and what resulted from it. Dean is unapologetic, telling Sam that as he is the only one who can wield the First Blade and thus kill Metatron, they will do things his way from now on. Dean then speaks to Castiel, asking him about the problem with his grace that Metatron had mentioned. Castiel confirms he doesn't have much longer, but hopes he has long enough to defeat Metatron though he is unsure of how to do that without his army. Dean tells Castiel he knows he was telling the truth about not sending the suicide bombers and while their force against Metatron is now down to just the three of them, Dean believes it to be enough as it always has been. To their shock, Gadreel arrives, but insists he's not there to fight but to defect, having realized that Castiel was right about Metatron and that Metatron must be stopped. When Sam asks why Gadreel should be trusted, Gadreel tells them he can give them Metatron as he knows where he is and what he plans and that the suicide bombers were really Metatron's agents. Gadreel understands that they don't trust him, but points out that like all of them, he's made mistakes and asks for a chance to prove himself to them. Dean goes to apparently shake Gadreel's hand, but instead slashes him across the chest with the First Blade, seriously wounding Gadreel.
Before Dean can kill Gadreel, Sam and Castiel restrain him and lock him in the Bunker's dungeon. They are able to locate the seriously wounded Gadreel and Castiel heals his injuries. Gadreel then joins them in their effort to stop Metatron, having been truly disillusioned of Metatron's plans by the suicide bombers.
With the help of Gadreel and Crowley, the Winchesters and Castiel go after Metatron as he attempts to convert humanity into following him instead of God. Though Castiel lacks his army, with Gadreel and eventually Hannah's help, he is able to break into Metatron's office in Heaven and break the angel tablet, destroying Metatron's God-like power. Without that and once Castiel reveals the truth of Metatron's deception to the angels, Metatron's own followers turn on him and imprison him, allowing the angels to retake Heaven.
- While Metatron's suicide bombing plan succeeds in turning Castiel's army against Castiel, it also has the side-effect of turning Gadreel against Metatron himself. This proves to be his downfall as Gadreel is able to use his knowledge of Metatron and position in his inner circle to help the Winchesters and Castiel defeat Metatron by themselves with minimal help from the other angels.