The episode picks up right where it left off last week, with Scott refusing to give Hayden the bite at Liam's request. However, it’s not because he doesn’t want to save her life-- it’s because he does, and at this point, Scott thinks she’s too weak to survive it (as was already implied by Peter Hale in De-Void)
However, Liam becomes so angry about this (since he believes Scott is now breaking the promise to do anything to save her that he made in Strange Frequencies) that his argument sends Scott into an anxiety-induced asthma attack. Theo has mysteriously procured another inhaler and tosses it to Scott, who takes a hit of it, too overwhelmed with everything to question it.
We then cut to Stiles, whose life is falling apart about as quickly as his beloved Jeep. When the Jeep’s engine overheats, Stiles goes to fix it with his new toolbox, but when he sees the bloody wrench he used as a weapon and loses his temper. Chucking the toolbox aside, Stiles then goes into his passenger seat, grabs the blood-soaked wrench he used to fight off Donovan and does the unthinkable: He throws it at the Jeep, shattering the windshield.
Meanwhile, at the police station, we’re hearing reports of a man/animal running around town, causing Deputy Clarke to total her car. She then runs almost an entire mile to the high school, which she then finds has been totally destroyed by this newest Chimera.
At this point, the supermoon is looming, and the Dread Doctors, who have also arrived at the school, remark that their success is “imminent," though this newest Chimera is still a mystery.
At the animal clinic, Melissa arrives to try some chelation therapy on Hayden, which is supposed to remove heavy metals from blood. However, the supermoon is already affecting Liam, who’s losing his mind over trying to save Hayden. Scott, however, has pretty much given up hope on everything and everyone, except for Theo, who is being extra-nice to Scott and who agrees to talk to the rest of the pack on his behalf to try to put them back together.
Back at the police station, Stilinski finds an envelope on his desk. In it, there’s a note from Melissa attached to Stiles’ library card. Apparently, the hospital maintenance staff is extremely meticulous and wouldn’t dare throw away something as valuable as a high school library card. Oh sure, the hospital maintenance staff is the one group of people in this town that is good at their jobs.
Also at the police station, Lydia is sitting and sort-of holding hands with Parrish through the bars of his cell as they try to figure out if he’s some kind of banshee. But when Parrish mentions the one time Lydia ever scared him—in the Season 5 premiere when Banshee-Spirit-Lydia tried to save him after Belasko nearly killed him—Lydia remembers the story Kira told her about the storm that night and the Wild Hunt. This gives Lydia an idea, and she bids him a temporary goodbye as she runs to the school library to do some research.
So, as Lydia leaves the police station, Stiles makes his way there. Malia gives him a ride after they watch the Jeep as its towed away.
Malia asks him if he needs a ride home, but Stiles instead asks to be taken to the Sheriff's station, because he has something he needs to confess to his dad. Once they get there, Malia, in a shocking twist, asks Stiles if he plans on telling Sheriff about Donovan, which shocks Stiles. Malia admits that she saw the bite on his shoulder and put it together, and adds that she never said anything because it doesn't matter to her. However, Stiles insists that it matters to him before getting out of the car and heading into the station, leaving a sad and confused Malia behind.
Once Stiles gets to the police station, things start heating up. Parrish is in the middle of a fiery dream that gets him so riled up that the temperature of the station starts to skyrocket. Just as Parrish wakes up with his orange-eyes glowing, Lydia is in the library at school, having just found an excerpt from a Bestiary of some sort that is about the Wild Hunt-- a myth of devilish riders in the night who are accompanied by black dogs, or "spectral beasts whose eyes glowed with fire." According to this, they are bearers of death and the guardians of the supernatural who are also known as Hellhounds.
Just as Lydia has realized that Parrish himself is a Hellhound, Parrish, in Hellhound-mode, breaks himself out of jail by using his thermokinetic abilities to melt the bars before leaving to go retrieve the newest bodies and take them to the Nemeton.
Back at the library, Lydia gets a Banshee-premonition and realizes that someone is going to die right there in that very room. Theo then suddenly appears behind her, correctly assuming that Lydia knows what is going to happen that night before knocking her out to ensure she can't warn anyone.
Afterward, Theo finds Malia in her coyote den while in his full-wolf form, which shocks Malia, who asks him how he did that. Theo assures her that he can teach her to full-shift again before bringing up that he knows about her plan to kill the Desert Wolf and that he wants to help her, because he knows Scott won't due to his feelings about murder.
However, when Theo asks Malia to come with him, he sneakily locks her up in a room in the wing that is currently under construction at the hospital, which serves to prevent her from interfering with his plans for Scott. He then throws away the key to the door before heading to the high school again, where he traps Scott in the library with a ring of Mountain Ash.
When Scott questions how Theo can touch mountain ash, he reveals himself to be the Doctors first ever Chimera-- part-Werewolf, part-Werecoyote. He commends Scott on his use of the word "chimera" to describe them, because not only does it mean "a creature with incongruous parts," but it also means an "unrealizable dream." Scott assumes that Theo must be the success, but, much to Theo's chagrin, he's forced to admit that while they came close to a success with him, he didn't quite making it, adding that "we can't all be True Alphas." Finally, he turns on Parrish's cell frequency jammers so Scott can't call for help, and bids him good luck with "what comes next."
Trying to escape, Scott runs up to the roof, but the exertion from trying to break through it gives him an asthma attack, forcing him to use his inhaler once again. He becomes so angry about Theo's betrayal that he squeezes the inhaler into a hunk of twisted metal in his hand, causing a purple vapor to burst out of it and revealing that Theo has been weakening him with wolfsbane-filled inhalers, which is why his asthma returned this season.
Scott looks up at the supermoon overhead when a growling noise alerts him to Liam's arrival, having presumably been let into the mountain ash barrier by Theo. Liam is already wolfed-out, and its clear that his first-ever supermoon (along with all of the stress of the last season) is making him even more aggressive than usual.
Meanwhile, when the chelation therapy does nothing to help (and in fact, has made her worse), Melissa and Mason sneak Hayden to the hospital and into the morgue that is currently under construction. and she’s only getting worse. Realizing that her death is imminent, Melissa sends Mason to go get Liam so he can say goodbye to his girlfriend, not knowing that he's in the middle of a smack-down, drag-out fight with his Alpha.
Weakened by the wolfsbane—and also trying to be a good Alpha due to his unwillingness to hurt his Beta—Scott doesn’t wolf out until he has to, telling Liam that he’s nothing but a pawn in Theo’s game who will be killed by Theo the second he takes Scott's power for himself. However, the supermoon's effects combined with his grief over his dying girlfriend have led Liam to believe that he wants to kill Scott himself, and continues to try to do so.
Also at the hospital, Malia finally breaks out of the room Theo locked her in to find a brand new Chimera, Noah Patrick, slurping down red bone marrow donor bags in the wing that is currently under construction. She immediately coyotes-out and starts to fight him, but when he extends bone claws from his wrists and hands and matches her in strength, Braeden suddenly appears and shoots him with her military-grade modified stun gun before asking "What the hell is that?" Outside of the hospital, Braeden informs her that not only does the Desert Wolf know she's alive, but she knows Malia wants to kill her and is now coming to Beacon Hills.
Elsewhere, Stiles is continuing to tail Parrish, who has just found and taken Corey and Beth's bodies from Sheriff's hiding spot, when he calls Theo for a ride. However, when Theo finally does show up, he learns the truth, starting with Theo showing him Stiles' library keycard. He snarks that even the son of the Sheriff can make stupid mistakes before pointing out that the Sheriff went looking for Stiles after he found it, but ran into Theo instead, and the tone of his voice and this veiled threat against his father's life leads Stiles to realize that Theo has been playing them all this entire time.
As Theo reveals, he came to town looking for Scott’s pack—only he doesn’t want Scott to be in it, he just wants Scott's powers and position as Alpha. He wants the werecoyote, Malia, whose first instinct is to kill; the banshee, Lydia, who is surrounded by death; the dark kitsune, Kira, and the Beta with anger issues, Liam. But, most of all, Theo wants Void Stiles. And in a very Dark Knight-esque twist, Theo tells Stiles that he’ll tell him where his dad is if he promises not to help Scott. In other words, Stiles can only save one of them.
Stiles then proceeds to violently punch Theo in the face multiple times, though Theo very much enjoys it due to his desire for Stiles to join him and use his darker impulses in his new pack. He remarks that this is the Void Stiles that he has been wanting so badly and asks him if he'll be saving Scott or Sheriff.
As expected, Stiles chooses his human father, leaving Scott to nearly be killed by Liam, who is only stopped from doing so by the arrival of Mason, who sadly informs him that Hayden died. Liam then leaves Scott brutally injured in the school's library as he runs to the hospital to go see Hayden.
Once there, he cradles Hayden's body in his arms and cries until Parrish, whose Hellhound-side seems to understand human grief, as he gives Liam one last moment to kiss her on the forehead before he takes her body to the Nemeton with the others.
As for Scott, Theo shows up to finish the job, briefly knocking Mason out by backhanding him in the temple and grabbing Scott by the front of the shirt. Scott reminds him that the rest of the pack won't join him, which Theo concedes might be true now, but he seems sure that they will eventually join him. When Scott insists that he's wrong, Theo takes this to mean because he's a Chimera and not a real werewolf, something that Theo is clearly insecure about, but Scott retorts that it's because he's barely even human.
This causes Theo to lose his temper and shove his clawed hand into Scott's gut before twisting it violently, thereby ruining any chance of getting Scott's Alpha powers for himself by having Liam do the deed. The red fades from Scott's eyes as he falls to the floor, and Theo turns to leave as Mason frantically crawls over to Scott's body.
By the time Melissa arrives at the school, Mason is kneeling over Scott with bloody hands as her son lays dead on the floor. Mason informs her that Scott has been without a pulse for more than fifteen minutes, but she’s not giving up on her son. Performing chest compressions, Melissa yells at her son to “roar," reminding both Mason and herself that Scott isn't a normal person-- he's her son, and an Alpha, and his time is not over yet. She becomes even more frantic as she beats on his chest with her fists, and after one last *thump*, the supermoon and the compressions finally work to bring Scott back to life for the second time, causing him to roar himself awake.
Meanwhile, Lydia wakes up in the Doctors’ operating theater, finally revealing what happened to put her in Eichen House— Theo used the memory sharing ritual on Lydia despite having never done it before in order to find the location of the Nemeton. While this does work as intended for Theo (in that he got the information he needed), it does not go as well for Lydia, whose eyes go blank from the trauma.
Grabbing the syringe of green serum from the Doctors’ tank, Theo takes Lydia out to the Nemeton to show her that if he injects just a little bit of the serum into the dead Chimeras, they will come back to life. He then does just that to resurrect Tracy, Corey, Josh, and Hayden are all up. When they are confused about what has happened to them, Theo informs them that they are his new pack, and he is their Alpha before turning and leaving Lydia laying in a catatonic state on the forest floor.
In the finale’s final moments, Melissa gives her son a pep talk about how he can get his pack back together if he just gives them hope. But this is easier said than done, especially considering that across town, the Doctors are breaking through a wall to reveal the “success” they’ve been looking for.