Corey and Mason are asleep in each other's arms in the tunnels beneath Beacon Hills. Mason shakes awake. Corey explains that he brought him underground because Scott can't track his scent down there. Mason doesn't want to accept that he's the Beast but Corey says he felt something after they turned invisible on the bus. It was Mason who figured out that transmissions and frequencies played a role in the Beast's manifestations. He then forces Mason to recall where he was during each of the Beast's appearances. Mason doesn't remember.

Mason realizes that the Dread Doctors can still track his unique frequency. They do, appearing in the tunnels and giving chase. The boys escape to the rain-soaked street above, where they are once again surrounded by the Dreads. Corey turns Mason invisible but the Surgeon strikes out with his cane and knocks him unconscious. The doctors take Mason.

~~~

Theo, Tracy and Deucalion discuss the Dread Doctor mask stolen from Valack's operating room . They want Josh to put it on since his powers are electrically-based and the properties of the mask are based in electromagnetism. Deucalion says the mask was originally manufactured by The Surgeon using "practices at the farthest edges of pseudoscience." The process harnessed electromagnetic fields in the masks "infusing them with a unique and deadly power."

Josh refuses to put it on.

~~~

Parrish is heading out of town. Lydia and the Sheriff want to stop him. The Sheriff reports that Parrish was spotted near the highway. Stilinski deployed a spike stripe. Parrish drives over it and it shreds his tires. The Sheriff is waiting nearby. Lydia arrives moments later. They both try to get Parrish to stay but he is adamant that, if he does, a lot of people are going to die. Lydia points out that her visions of death don't always come true. The Sheriff adds that him leaving might be the cause of the deaths he's been seeing, because he wasn't around to protect them.

~~~

Scott is still recovering from his run in with the Beast. Kira helps him to bed where he sees his application for a scholarship. He failed to send it in before the deadline. Kira says they'll figure it out but first he must heal. Stiles enters. Kira nods. Stiles closes the door.

In the hallway of the McCall, Malia and Braeden inform Stiles that the Desert Wolf may want to kill him too. He asks for a gun and makes his case that he should have one. Braeden removes the clip from her pistol and tosses it to Stiles. He bumbles it and drops it to the floor. He decides he shouldn't have a gun.

~~~

Liam and Liz are looking for Mason in the woods. They find Hayden instead and they set out together to find their friend.

~~~

Scott wakes up the following morning fully healed. Kira, Malia, Liam, Cheryl, Reed, Liz, Lydia and Stiles are in the kitchen discussing the search for Mason. The sheriff has issued an All-Points Bulletin (APB) for Mason. Liam still thinks his friend might not be the Beast. Hayden is at school looking for him. Malia volunteers to search the woods while Scott joins the conversation and says his mom can check all the hospitals in the county. Scott says they will find him and figure out a way to save him.

Lydia wants to know where else they can look. Scott says they should ask Corey and, reaching behind him, yanks the invisible boy forward. Corey becomes visible and explains that the Dread Doctors have Mason.

"Wait! WAIT! It's not my fault! They took him, and I couldn't do anything. They took him!" Corey explains.

"Who?" Scott asks.

"The Dread Doctors." Corey answers.

"Well, that complicates things" Selene says as she walks into the house with Brett.

"You alright?" Scott asks.

"Yeah. But there's something I gotta tell you first" Selene replies and sighs.

~~~

Mason hits the floor in the Dread Doctors Lair. He props himself up next to the bubbling tank with the body inside. They attach a long, glowing tube with a needle to the back of his neck. Mason screams in pain.

~~~

"So the story Gerard told me isn't right but he thinks it is?" Lydia asks.

"Yeah. Well, most of the story is true but it just misses one person" Selene explains.

"So you're telling us that your dad... helped kill the Beast the first time it was around?" Stiles asks.

"I am. He was a friend of the Valet family and when Sebastien came back from the War... he knew something was wrong. Then after everything happening with La Bête, he knew it was Sebastien. He also knew that Marie-Jeanne wouldn't believe it" Selene explains.

"She didn't believe in the supernatural, of course, she wouldn't believe her brother is the creature that had killed children in their town" Lydia realises and Selene nods.

"Exactly. He knew Henri too, he even helped him gather everything. So he asked Henri to follow the hunting party and use the Mountain Ash and wolfsbane to protect Marie-Jeanne. My dad explained everything to Marie-Jeanne but she still couldn't believe it was her brother. So they did the test with Rowan berries and in that moment Marie-Jeanne believed" Selene continues.

"Why doesn't Gerard know this?" Scott asks.

"I'm getting to that. My dad explained he was a Kitsune and that he was over two thousand years old. While brainstorming about the weapon he is the one that came up with the pike. Marie-Jeanne and Henri agreed but Marie-Jeanne wanted a back-up plan. She knew that maybe she would die before killing her brother so..." Selene sighs. "She asked my dad to make a promise. A promise to kill the Beast if she couldn't. He made the promise and they made a weapon" Selene transforms her belt into her sword and puts it on the table.

"So your dad's sword can kill the beast? Why haven't you yet?" Kira asks.

"Because I didn't want to kill the teenager if there was still a chance to save him. And that chance is still there" Selene explains.

"Wait, why didn't Gerard know about this?" Scott asks.

"Because Marie-Jeanne wanted to make sure her brother wouldn't know. And even after they died they wanted their kitsune friend to be safe" Selene explains.

"Okay, let's go save our friend" Liz says.

~~~

Tracey brings Theo the jar of garuda talons he got from the Desert Wol. Theo says they're useless unless they have the beast. Deucalion says they're just useless as he explained to Hayden. He suggests that Hayden and Corey have deserted Theo.

Josh steps up and says he's leaving. Tracy blocks him. Deucalion continues to play on his theme of Theo's dwindling pack. He orders Tracy to paralyze Deucalion's tongue. Before she can, he turns his manipulations on her. He questions her about how powerless she was before her transformation. He says the truly powerless are always all too willing to demonstrate their newfound strength.

He then shows that he's been a willing captive all along. Saying again that he wants Scott McCall's and Selene Vulpes' eyes, he tears out the wolfsbane drip attached to his arm and explains that he "let" them take him in the first place.

~~~

Kira's dad warns her that putting her sword back together would be dangerous. She argues that she needs her sword. He argues that the sword, although it brings out her fox spirit, is just a weapon. She is the critical part to saving her friends but needs to find balance. She says she has "800 years to find balance" but needs to help Mason immediately. Mr. Yukimura explains that Kira's sword was forged with a "unique power" and it takes a unique power to put it back together and that Kira will need help.

~~~

Deucalion says he'll show Theo how to take the power of another werewolf. He begins by breaking Theo's arm. He explains that pain is the secret to taking power. "Take their pain, take their life, take their power." "You take till there's nothing more to give. That's where you find the spark of power. Then, you take that as well. Pain, life, power in that order and only that order." Theo resets the bones in his arm and says he understands "perfectly." He then jabs his claws into Josh, taking his power and killing him.

Deucalion points out that he just cost himself another member of a "small and inexperienced pack." Theo turns to Tracy and asks what she thinks. She says Josh was "small and inexperienced." She also points out that, with Josh's power, Theo can now wear the Dread Doctor's mask.

~~~

Parrish and Lydia return to the Nemeton. Parrish flashes back on his dreams. He touches the tree. Lydia touches his arm and Parrish has a vision of her death at the stump. An orange glow begins to suffuse the rings of the tree.

~~~

Deucalion encourages Theo to put on the mask saying the kind of power he seeks requires risk. He tells him to "discover the beast's identity and guarantee your place as an Alpha, as a real werewolf." Theo puts on the mask and begins to scream.

~~~

Scott, Selene and Liam are walking down the hallway toward the locker room while they talk about what they're about to do.

"How stupid are we to be doing this?" Liam asks.

"We're not stupid. We're desperate" Scott corrects him.

"How desperate?" Liam asks. Scott stops just as he's about to push the locker room door open and sighs.

"Incredibly desperate." Scott answers. Selene shakes her head and opens the door. The two walk into the room, where they find Theo and Tracy waiting for them. Theo looks smug at the fact that they've been forced to come to him.

"I told you we'd end up on the same side" Theo states smugly. Liam and Selene have an identical fake smile.

"How about I punch you in the balls to remind you we're not?" They say in unision. Theo genuinely laughs at this remark, but Tracy just scowls at Scott and Liam.

"I love this kid!" Theo says about Liam.

"I don't" Tracey says irritatble.

"We know you're not on our side, Theo. You said you wanted to help Lydia, but you left Eichen with something else, didn't you?" Scott asks.

"You mean the mask? Are you worried about that?" Theo asks.

"Did you put it on?" Scott asks. When Theo just smiles, Scott takes this as a "yes" and continues on. "Who did you see?"

"Not Mason" Theo replies.

"What does that mean? It's not him?" Liam asks confused. Tracy smirks rudely at them.

"It probably means he's a lost cause" She taunts

"I will actually stab you in the face" Selene threatens with a bored look on her face.

"We all want the same thing. We want Mason back" Theo quickly interrupts before Tracey can try to kill Selene.

"Okay, but the difference is that we want him back alive." Scott says with a scoff.

"Well, I'm open to compromise. You still got the map with the telluric currents on it?" Theo asks. Scott looks wary about this question, but ultimately nods. "Bring it to the operating theater in two hours"

As Liam and Scott walk out of the locker room, Liam gives Scott a skeptical look.

"How desperate are we?" Liam asks.

"Incredibly." Scott repleis with a sigh.

Deucalion is also in the locker room. After Scott, Selene and Liam exit he explains that Theo and Tracy will need them if they want Mason to trust them. He says Theo can only take the power from the beast, not from Mason, which means they'll need to get up close after he transforms. Theo says Tracy will need to paralyze him. She argues that her venom didn't work on Parrish. Deucalion says that's because he is a Hellhound but the beast is still a werewolf.

~~~

Stiles, Lydia and the Sheriff discuss the merits of using Theo to help find Mason. They all agree that he is also using them. Stiles says they're covering all the places Mason could show up. Malia, Cheryl, Reed and Braeden are at Scott's house. Melissa is covering the hospital while Hayden and Corey are at school.

~~~

Josh's body has apparently been disposed of prior to Scott, Selene and Liam's arrival to the operating theater as requested, likely because they'd be unwilling to help if they knew what he had done to Josh. Theo is standing alone in front of the now-empty tank where the body was previously held in green fluid as Scott and Liam join him.

"They called him Der Soldat. That's German for "The Soldier." I'm pretty sure he fought in World War II" Theo explains and Selene gives him a look like 'You think we're stupid?' when he translates 'Der Soldat'.

"And he was a Nazi?" Scott asks

"No he was a German American" Selene states sarcastic rolling her eyes. Theo smirks.

"And an Alpha werewolf. The Dread Doctors were using him to prolong their lives. They've been doing it for decades. Actually, probably longer" Theo explains.

"How old are these guys?" Liam asks confused.

"Who knows? But wherever they go, he goes, too"

"So how do we find him?"

"Keeping him alive requires a pretty unique set of conditions. There's got to be a power source, it has to be underground..." Scott, realizing where Theo is going with this, reaches into his jacket pocket and pulls out the map.

"...And on a telluric current" Scott realises. Scott hands Theo the map, causing the Chimera to smirk in satisfaction, which causes Selene to growl.

"Looks like we're going for a hike" Theo states. Neither Scott, Selene nor Liam seem to have a good feeling about this plan.

~~~

A teenager comes into the hospital with severe injuries. Melissa thinks for a moment it might be Mason but it's not.

~~~

Malia, Reed, Cheryl and Braeden are at the McCall house. Braeden has established a Mountain Ash barrier to keep the Desert Wolf out but Malia feels trapped and says she might lose her mind. Lydia, by phone from the Sheriff's office, explains that the ash is there to keep her safe. Malia says she should be keeping Stiles safe.

Outside the Sheriff's Station, The Desert Wolf is listening to their phone call.

~~~

Hayden and Liz try to comfort Corey at school.

~~~

Braeden is eating pistachios. As she shells them, she arranges the half shells in a straight line along the table.

~~~

Lydia, Stiles and the Sheriff wait for word at the Sheriff's Station.

~~~

Theo, Selene and Scott are leading the search party while Liam, who knows Mason's scent best, follows behind. After a moment, Scott glances over at Theo and gives him a knowing look.

"Where is he?" Scott asks.

"I thought we were looking for him?" Theo asks, playing dumb.

"You know who I'm talking about"

"Deucalion?"

"You shouldn't trust him" Theo shoots him an exasperated look."And you're the ones who let him live"

"We're not murderers"

"You still think you're gonna get through this without killing anyone?" Scott rolls his eyes in annoyance.

"I didn't say that" Just then, Liam stops walking, leading the other three to stop as well."We're close" Liam states.

"You get his scent?" Selene asks. Liam nods worriedly, which visibly interests Theo.

"Which way?" Theo asks. Liam glares at Theo before turning to Scott and Selene, clearly unwilling to trust him enough to share this information. When Theo realizes this, he scoffs again in frustration."You think you're going to leave me behind?" Theo asks

"You know what Theo? Why don't you tell us how you killed Josh for his powers? Yeah that's right, I know. I can feel the electricity radiating off of you" Selene finaly snaps. She shakes herhead and sighs, turning to Scott. "Look, he wants to kill Mason-" Theo cuts her off and interjects.

"I just want his power! You want to fight someone that actually wants to kill Mason? Go fight Parrish" Liam continues to glare at Theo.

"Who did you see when you put on the mask?" Liam asks.

"I already told you, it wasn't Mason" Theo says.

"Who was it?"

"I saw a man dying in the snow. He was impaled on a spear" Theo replies.

"It's called a pike, idiot" Selene corrects him.

"Then you know what it means. Time's running out" Theo pints out. Selene seems visibly disgusted by her next words.

"I really hate to say this, and even though I don't trust him... He's right" She admits. Theo turns to Liam, who still does not look pleased.

"Where is he, Liam? What direction?" Theo insistes. Liam sighs and looks at Scott and Selene for advice. When Scott shrugs and Selene, reluctantly, nods, Liam answers his question.

"This way" Liam replies. The four keep walking and following Mason's scent until they come upon a small cabin in the middle of the woods. Liam is eager to go inside, but Scott grabs him by the wrist to stay his hand when he tries to open the door.

"Listen" Scott insists. They all focus their hearing and pick up the sound of a heart beating relatively quickly, which Liam immediately recognizes.

"It's him" Liam says. They rush inside the cabin and down the steps, with Liam leading the group."Mason?" Liam calls out.

They make it down and are all relieved to find Mason sitting on the floor with his head dropped down toward his knees. His back is leaning against the large green tank with Der Soldat floating inside it. However, when they crowd around Mason, their relief turns to horror when they realize something is wrong with him. Mason is breathing quick, shallow breaths as Scott's eyes travel from the plug in his neck to the tank and realizes what is happening.

"It's connected to him..." Scott realises.

~~~

Kira leaves a voicemail for Scott explaining that she has to leave to help find a way to save Mason but that she will be back to help.

~~~

Scott, Selene and Liam are still nearly around the half-conscious Mason, trying to figure out how to disconnect him from the plug in his cervical spine while Theo stands nearby and watches impatiently.

"What is this thing?" Scott asks.

"I don't know" Theo replies. Just then, Mason briefly comes to and weakly calls out to his best friend.

"Liam, I can feel it... It's in my skull" Mason tells them. He whimpers in pain but keeps his head dropped down so that his chin is against his chest, and Scott, Selene and Liam look panicked and at a loss for what to do as they continue to examine the plug.

"Don't move" Liam tells his best friend. Liam reaches his hand to touch the plug in Mason's neck.

"Careful" Selene warns. Liam looks up at Theo with a horrified expression.

"What are they doing to him??" he asks the chimeara.

"I don't know!" Theo replies.

"Guys, focus" Selene says. Scott moves so he's in front of Mason to look him in the eyes as best as he can.

"Mason, we're gonna get you out of here" Scott tries to reasure Mason. Mason nods weakly as Scott turns to Liam, though it's obvious that Scott is concerned that he has no idea what they're doing. "Hold him still" Scott moves around so he's behind Mason in preparation to try to unplug Mason from the tank. "Okay. All right. I'm going to try to pull it out. Let me know if it hurts"

Liam holds onto Mason as Scott reaches for the plug, wrapping his hand around the base of it and holding Mason's neck with his other hand to stabilize it. However, Mason starts to moan loudly in pain as soon as Scott grabs it, and Scott quickly lets go.

"AHHHH! It hurts!! It definatly hurts" Mason says. Scott immediately lets go out of fear of hurting Mason more and looks at Liam apologetically, though it's obvious that he's extremely worried about their current situation.