Mason (Khylin Rhambo) is no longer a sidekick on “Teen Wolf” Season 5B. But it’s hard to say what exactly he is. Last week, he was revealed as the Beast before escaping from the pack. In episode 19, the group decided to find and save Mason, even though they didn’t really know how to do that. However, Mason’s time may have run out on the MTV drama.

The episode kicks off as Mason wakes up in the tunnels and tells Corey (Michael Johnston) that he isn’t even a candidate for the Beast. Corey quickly makes him realize that he can never remember where he is during the Beast attacks, and Mason is shocked that he was the chimera that he has been searching for. However, the Dread Doctors are also looking for him. They’ve found him and Corey, and they have to run for their lives. The Dread Doctors catch up quickly, and the boys can’t escape. They injure Corey and kidnap Mason.

Meanwhile, the chimera pack is still in the dark about the Beast’s human persona. Theo (Cody Christian) wants Zach (Henry Zaga) to put on the Dread Doctors’ mask to find out the Beast’s true identity. The mask’s powers are based in electromagnetism and Josh’s electrical powers mean he might be the only one to survive wearing it. He isn’t willing to take the risk, though, much to Theo’s dismay.

Elsewhere, the Sheriff (Linden Ashby) and Lydia (Holland Roden) try to stop Parrish (Ryan Kelly) from leaving Beacon Hills. “You said you were drawn to Beacon Hills. I think you’re here for a reason,” Lydia says. The Sheriff gives him back his badge. Later, Lydia brings Parrish to the nemeton and tells him that he can “save them all.”

Malia (Shelley Hennig) tells Stiles (Dylan O’Brien) that she believes her mother, the Desert Wolf (Marisol Nichols), will go after him. Since he can’t be trusted with a gun, he’ll have to rely on his supernatural friends to protect him. However, they have other concerns. They need to find Mason.

Scott wants them to track him down and figure out a way to save him. Once he says that they’re saving Mason, Corey reveals he was hiding in the room. He explains that the Dread Doctors have their friend.

The chimera pack’s meeting isn’t going quite as well. Deucalion (Gideon Emery) points out that Theo’s pack is falling apart, which means they can’t uphold their word. They promised him Scott’s eyes. He pulls the tube out of his arm and reveals he hasn’t been a hostage at all. He has been a willing guest, and now he wants to teach Theo something. He attacks and breaks the chimera’s arm. The older wolf explains that Theo has to take his enemies’ pain, life and power. Theo attacks Zach and kills him. He is down another follower, but he has the electrical powers now.

The wolf encourages the newly empowered chimera to put on the mask. When it’s on, he starts screaming in pain. Theo turns out fine, though. Scott even turns to him for help later. Theo agrees to search for Mason if they give him the map with telluric currents.

Deucalion comes out of the shadows after Scott leaves and says they need Mason to trust them. He clarifies that their plan uses Tracy’s (Kelsey Chow) venom to paralyze him, which might weaken him enough for Theo to kill Mason and steal the Beast’s power.

Theo takes Liam (Dylan Sprayberry) and Scott into the woods. Liam picks up Mason’s scent and follows it down to an underground laboratory. Mason seems to be hooked up to a chamber holding another body via a tube in the back of his neck. When Scott tries to remove it, Mason cries out in pain.

A Dread Doctor finds them and tells Theo that he keeps making the same mistake. “We’re taking Mason and I’m taking what’s mine,” Theo says. Theo confronts the Doctors, who taunt him by calling him a typical, narcissistic millennial. They call him ordinary.

“From you we learned that true evil only comes by corrupting something truly good,” the Doctors tell him. The Doctors take on Theo, Liam and Scott. While they fight, Mason takes the tube out of his neck. He starts to transform without the frequency trigger that the Beast has always needed before.

“Mason!” Liam calls.

“Is not my name,” Mason says as his eyes glow blue.

The Beast rips apart the Dread Doctors and injures Theo. As the Beast goes outside, Parrish (who is engulfed in flames) attacks. The Argents start shooting. When the Beast goes back to human form, Sebastien (Gilles Marini) appears instead of Mason. Audiences had previously been warned that once the Beast remembered his life as a man, the present-day teenager would be gone. Will the pack find a way to bring Mason back?

Scott goes back to his house quickly. Malia is in trouble there. She notices that the mountain ash line is broken and knows they’re in trouble. The Desert Wolf is there, and she faces off with Braeden (Meagan Tandy). After the Desert Wolf gets knocked down, Braeden runs off. The assassin gets up to find that Braeden fixed the mountain ash barrier. The evil werecoyote is caged in the house with her daughter, and neither of them can escape.

Elsewhere in “Teen Wolf” Season 5B, episode 19:

  • Kira takes the pieces of her sword and leaves town, saying she is going to help save Mason. She goes to the desert to ask the skinwalkers for help. She says she’ll do whatever it takes. “We can help her, but it comes with a price,” the skinwalkers say. “Everything has its price.”
  • The Argents might have a cure for Mason, but they aren’t telling Scott everything they know.
  • Scott’s mom (Melissa Ponzio) figures out how Mason is a chimera. Mason absorbed his twin when he was in the womb. That makes him eligible to be a genetic chimera.

The “Teen Wolf” Season 5B finale airs Tuesday, March 8, at 9 p.m. EST on MTV.