- "I am the Alpha of Alphas. I am the Apex of Apex Predators! I am Death, Destroyer of Worlds! I am the Demon-Wolf! Hate it when that happens."
- ―Deucalion to his pack[src]
Sometime in 1977, Alexander Argent is hunting down Deucalian or the other way around but Deucalion ends up biting Alexander, who later takes his own life for his code. 
A pack of werewolves led by Ennis approaches the distillery. Ennis shows the werewolves with him a rope covered in blood hanging from a hook in the distillery ceiling. Deucalion and Kali are among the group. Ennis says the hunters dragged one of his wolves here with an arrow in his throat. They hung him up and cut him in half. "They killed one of ours." "One of yours," Kali says. She wants to know why she should care about someone from another pack dying. Another werewolf points out that hunters don't discern packs. Deucalion adds that they do discern motive. Deucalion asks Ennis why his pack member was killed, and one of Deucalion's pack says that Ennis's young and naive beta killed a hunter. Ennis says it was accidental. A wolf howls outside the distillery, and then a black wolf trots into view. She shifts into human form, and one of the wolves from another pack puts a blanket around her shoulders. She gives Deucalion a smirk and a knowing look. Talia tells the other wolves that "It's his right. We're not the only people to adhere to rituals thousands of years old." Deucalion argues that tradition is no reason to keep doing something. Ennis says that the hunters have not evolved so neither should they. Deucalion tries to convince him not to carry a vendetta. A blood feud with the Argents won't end with an eye for an eye. A murder will become a massacre. Ennis doesn't listen and carves a revenge spiral into the side of the distillery. Talia and Deucalion look worried. Sometime later, Deucalion and Talia are in a meeting with Deaton. He says that their willingness to extend an olive branch to the Argents is admirable, but Talia thinks Gerard is unlikely to accept it. Deaton thinks that Talia means it's the matriarch of the Argents who they should be dealing with, but she clarifies that she just meant Gerard is a psychopath. Deucalion is surprised that they have so little faith in humanity. "You think that Gerard isn't worried about the deaths on his own side?" Talia advises Deucalion to meet Gerard and neutral ground and not to go alone. Deucalion replies that he's an alpha, so he never walks alone. Deucalion and his pack and Gerard and his hunters meet in the distillery. Gerard thinks this is a fitting setting because distillation is the separating of two substances by pushing them into their volatile states. Deucalion says that he was hoping to avoid volatile. Gerard then turns a crank and blasts them all with steam with something in it, perhaps wolfsbane. Gerard gives himself a shot of something to protect from the effects. While the werewolves are incapacitated, Gerard picks up a spiked mace that he stashed in the building. He starts attacking his own hunters, killing them in a way that will look like werewolf kills. Deucalion can't believe it. Gerard's people wanted peace too, which he would not allow. Deucalion crawls out of the distillery, coughing. He rolls onto his back and looks up at Gerard begging him not to kill him. "I had a vision, a vision of peace." Gerard smirks and jams two arrows into Deucalion's eyes. They might be flashbomb arrows from the sparks that shoot out. Deucalion wails in pain. At the Animal Clinic, Deaton unwraps the bandages from Deucalion's face. Deaton tells him that his eyes will heal physically but his sight will be gone. Deucalion roars and collapses against the table. He orders the others to leave him alone, and Talia and Deaton leave. Deucalion's second, Marco, remains in the room with him. Deucalion tells him again to leave him alone, and Marco replies that he is alone. Marco attacks him, and Deucalion learns that he can see with alpha vision. He attacks Marco in return and tears him apart. 
Deucalion finds Omegas Ethan and Aiden and has taught them how to meld together forming one massive werewolf. After he taught them to do that, they had enough power to kill their alpha and their old pack. 
After taking up residence in an abandoned bank in Beacon Hills, Isaac comes snooping around where the alpha pack has taken up residence. He discovers that he is keeping Boyd, Erica and another unnamed women hostage inside of the vault. Later, Scott and Isaac walk further into the mall where Deucalion has already arrived. Derek is already there and shifted. It’s revealed that the rest of the alpha pack is also at the warehouse, but so are Boyd and Cora.
Scott meets Deucalion in the elevator at Deucalion's apartment. He immediately unsheathes his claws. Deucalion taunts him and tells him that he may find himself in a situation where he has to kill someone to protect another. Deucalion reveals that he lives in the building and he wants to see what Scott’s made of. Derek makes the first move by running at Deucalion before being intercepted by Kali. Boyd takes on Ennis while Isaac goes for the twins in their combined form, and with resignation, Scott shifts and joins the fight. Deucalion simply watches as his pack takes on the Hale pack and Scott is shown receiving the torso wound that Allison had to stitch up. The alpha pack brings the fight to a stand still, and Deucalion delivers the ultimatum that Derek must kill Boyd, but the others will be let go. Derek hesitates, and Kali tells him that he must choose between pack or family while shifting her position on top of Cora, making the bones in Cora’s neck creak. As Derek struggles to make a decision, Allison appears with flashing arrows. 
A blind man enters the elevator with Scott and later asks Scott to help him out of the elevator. In the locker room, Deucalion uses his hand to create a mental picture of the girl. She tells him that he’s afraid of the teenage boy, implying that Scott is a threat. Deucalion replies that he is a potential threat, but he’s planning on having someone else take care of that threat for him, and the girl realizes that he means Derek before Deucalion kills her. 
The alpha pack goes to Derek's loft where Kali jams a pole through Derek's stomach. Deucalion then walks in. Deucalion tries to talk to Derek as the female alpha, Kali, twists the pipe through his back. The other alpha lets Cora up, but she knows better than to try to rush to him at this point. Kali continues twisting the pipe in Derek’s back. Blood is dripping from Derek’s mouth. Deucalion wants Derek to kill one of the members of his pack. Derek’s condition is beginning to visibly worsen as Deucalion continues his discussion of the alpha pack. Cora is beginning to look very worried. Deucalion shares that when an alpha kills one of their betas they absorb the beta’s power. Apparently Deucalion found this out accidentally, but ended up killing all his betas once he realized. Deucalion remarks that Derek looks like his mom before beginning a rant that he is the "Alpha of Alphas", the "Apex of Apexes", the "Predator of Predators", "Death, Destroyer of Worlds", and "The Demon Wolf," complemented by dramatic lightning although there is no evidence of a storm happening. As his rant culminates Deucalion’s sunglasses shatter. Kali pulls the pole out of Derek’s back, and the alphas leave as Cora rushes over to her brother. At the school, the twins prepare to fight Scott and Isaac, merging together. They don’t make it far before getting caught. Deucalion appears and the twins separate, knowing that they've been caught. Deucalion slices them both on the cheek with the blade in his cane before leaving. The twins follow him. 
Deucalion arrives at the animal clunic and talks with Deaton before crushing Ennis’s skull with one hand. Deaton is more than a little disturbed. Outside, Aiden and Kali exit the clinic. Kali roars while held back by Aiden. 
Scott is hallucinating and Melissa McCall calls Scott and tells him to look outside. Scott goes to the window and sees Deucalion holding her by the throat and telling him that he's an alpha now. Deucalion then rips Melissa's throat out. 
At the hospital, Deucalion is with one of the alpha twins. The alpha twin speaks into the Demon Wolf's ear perhaps telling him what's going on. Chris Argent stands in the background watching them. The following day, Deucalion taps on the piano at the school to try and distract Scott and to lead him to him. He changes beat when Scott enters. He asks Scott if he knows what a metronome is. He doesn't wait for an answer before telling Scott it's an instrument to keep rhythm. He tells Scott that the tempo in his life has sped up the last couple of hours. He offers to help Scott find Deaton. Scott is angry, and Deucalion offers Scott a challenge. If he can get the cane away from him, Deucalion will tell him where Deaton is. Scott puts up a fight, but Deucalion then slashes him with the blade hidden in the tip of his cane and explains that he is not behind the rash of ritual murders, saying he’s not the one praying to ancient gods or gathering herbs or "whatever the hell druids are supposed to do." Deucalion admits he is part of the pack that wants Derek dead and that Kali is coming for him. He says Scott will have a difficult choice to make. Someone is going to die, Derek or Deaton, and the decision is up to Scott. Deucalion leaves him with a cryptic clue: "Let the currents guide you." 
Kali and Deucalion enter the hospital and walk right by Melissa. The elevator dings open, and Jennifer walks into the same hallway as Kali and Deucalion. Deucalion takes the tip off his cane, revealing a blade, and throws his cane like a javelin at Jennifer. It impales the wall next to her head. Kali makes a run for the elevator as Jennifer tries to escape. She catches the doors before they close, but Jennifer summons up some magic and repels her away from the door. Melissa finds Deucalion's cane stuck in the wall. She pulls it out, and then Deucalion eases it from her hands. "Thank you, Ms. McCall." She knows who he is. "The bad guy." He replies, "You have no idea," and both his and Kali's eyes glow red. Deucalion then uses Melissa to get to Scott by speaking through the speaker. On the roof, Melissa asks Deucalion what he wants with her. "You're my gesture of goodwill." He tells her to go find Scott and lets her leave. Kali and Deucalion are in the morgue. Kali argues that he should have kept Melissa. She thinks Duke has a soft spot for Scott. "I have an investment I'm trying to mature," he says. He then tells Kali that if she wants to talk about soft spots they can talk about Jennifer Blake. That gets Kali to back off. She calls Ms. Blake by her real name, Julia Baccari. Kali tells Duke that she didn't understand why she had to kill Julia, too, since she was harmless, but she did it because Deucalion asked her to. "I did everything you asked to be a part of this pack." He counters that she really did it to be with Ennis and that Julia isn't looking so harmless now. Kali thought Julia was dead. She says there was a moment of uncertainty when she turned back and saw Julia lying perfectly still but focused her hearing anyway. "Listened to the sound of her heart still beating, still fighting for life, and I thought, 'I could go back and finish it, or I could let someone I love die peacefully.'" Kali asks Deucalion what Scott and his friends are doing. "Plotting," he replies, looking amused. Scott races to the roof. "Mom! Mom!" "They're gone," Deucalion says. "Guardians, Scott. If you were with me, I could've told you what it meant. I could've warned you." Deucalion makes Scott an offer. If he helps him catch Jennifer, Duke will help Scott get their parents back. Scott wavers and starts to cry. He gives in to Duke. Stiles arrives and begs him not to go with the alpha pack, but Scott doesn't know what else to do. "Scott, there's gotta be something else. We always--we always have a Plan B." Scott shakes his head and goes with Deucalion, promising Stiles that he'll find his dad. 
Deucalion and Scott are in the woods. With his alpha vision, Deucalion sees a bright light glow and then die. Scott tells him it was a firefly. "Unusual for this region," Deucalion says. It's the second time someone has pointed out how odd the fireflies are. Scott asks him if it's because of Jennifer. The animals started acting weird just before she started killing people. Duke suggests that maybe animals can sense supernatural disasters as well as natural ones. Deucalion walks into the clearing and wants to know how Ms. Morrell knew they'd come for her. She says that she and Jennifer are the same and that she knew Deucalion had always been suspicious of emissaries. Kali adds that it's with good reason, because she sent Braeden to get Isaac. Ms. Morrell maintains that she did that to maintain balance. She then turns to Scott and tells him that this isn't him. Ms. Morrell tells Scott to go back to his friends. Duke replies that Scott can make decisions for himself. She asks Duke if he's told Scott everything he's done. "How you've piled up bodies in a narcissistically psychotic effort to form your perfect pack? Bodies that include Ennis, by the way." Morrell looks at the pack as she says this and explains that Ennis was alive when Deucalion went in to see him. 
Allison, Isaac, and Scott meet up with Deucalion at the overlook point. "Cutting it a little close, aren't we, Scott?" Duke asks. Scott wants to know where the other alphas are, and Duke tells him they're occupied. He thinks he and Scott will be enough, though. Scott and Deucalion wait in the distillery for Jennifer and Derek. Scott clearly wasn't expecting Derek to be there with her. "What are you doing?" "This might be hard to believe, but I'm actually trying to help you." Deucalion finds the brother against brother theme very American. He puts away his cane and asks Jennifer if she gathered her herbs and prayed to her ancient gods and her oak trees. "Should we show them why you needed to sacrifice nine innocent people just to face me?" As he speaks, Deucalion starts to shift. His skin goes black, and he eyes glow red. Derek attacks Deucalion, but Duke just grabs his arms and holds them down. Jennifer takes her shot, attempting to hit him with the same force punches that she used on the others, but the power just skirts around him. Duke them grabs them both by their throats and lifts them up. He tosses them, and Derek tries to attack again. Duke hits him with one blow, sending him across the distillery and into a stack of tires. Duke backhands Jennifer and then grabs her by her hair. He brings her over to Scott and orders him to kill her. When Scott hesitates, Deucalion alpha roars at him, bringing Scott to his knees and forcing him to shift. Duke tells him that the parents are dying because the the storm Jennifer has conjured is burying them alive. "Kill her, and it ends." Duke rushes over to Scott and grabs him by the back of the neck. He forces him to walk to Jennifer. "Maybe you just need a little guidance." Scott tells Deucalion that he forgot to tell him something. "Something that Gerard told me. 'Deucalion isn't always blind.'" Scott slips the flash bombs out of his pocket and throws them all on the ground. All three wolves stagger around. The lunar eclipse then hits, and the three of them shift back to human. Scott gets up to find Jennifer missing. Jennifer returns to the distillery in Darach form. Derek hides behind a stack of crates. Jennifer attacks Scott, tossing him back, then goes after Deucalion. She bashes his head into the floor repeatedly. Derek jumps up from his hiding place and calls her name. "He doesn't know." "Know what?" "What you really look like. He knows the cost of bringing Kali into his pack, but he's never seen the price you paid." She agrees that he hasn't, so she heals Deucalion's eyes. When Deucalion turns to her, he still sees her glamor. She goes to strike him but falters and collapses. "What is this?" she asks Derek as he catches her. He explains that healing Duke made her weak. She won't have her strength back for a few minutes. "Then you do it. Kill him." "No. Like my mother used to say, I'm a predator. I don't have to be a killer." Then he grips her throat and orders her to let the parents go. She shoves him back and hits him a few times in the face, looking betrayed. She leaves him and turns back to Deucalion, but he gets up and goes after her again. Deucalion gets up from the floor as Scott tells Jennifer to stop the storm. Scott declares that if she doesn't stop the storm, he'll kill her and he doesn't care about the color of his eyes. "It won't change the color of mine, so allow me," Duke says. He rushes forward and slashes her throat. Derek and Scott face Deucalion. "My mother told me you were a man of vision once," Derek says to Duke. He looks at Scott, who urges him to say what he doesn't really want to. "We're letting you go because we hope you can be that man again." Scott adds, "But if you're not, then having your eyesight back won't matter, because you'll never see us coming." Derek and Scott leave Duke at the distillery. 
Losing His Sight, Again
A short while after his encounter with Scott, his eyesight reverts back to its original state.
Deucalian is found by Theo and his Chimera Pack. Deucalian manages to take down most of the pack but is eventually subdued and is brought to the Dread Doctors lab. When Theo arrives, Deucalian is being injected by a substance that seems to be keeping him weak. Deucalian vows to take revenge on Scott McCall.
Hayden is keeping Deucalion company. He tries to get her to unshackle him but she refuses. He tells her that he will tell her about the talons on the table if she sets him free. He says he knows the talons were created by the Dread Doctors and that Theo is crazy if he thinks he can use the talons to absorb the power of the beast. The Dread Doctors designed the Talons for someone else. If Theo puts the talons on they will kill him.