Everyone knows a Lin Bei Fong. Maybe its a grandparent, an aunt or uncle, a school teacher or a neighbor. Someone surly, curt and enigmatic, a perpetual grump whose bark is equally as vicious as his or her bite. Mine taught high school American History, ruthlessly. Her method resembled 'Full Metal Jacket.' It worked, with minimal psychological damage. At the time, students either loathed her or loved to loathe her. And that was that: She was just an angry old lady.

Years later, I learned that her past was littered with hurdles: Familial turbulence, the death of her husband, and her own health problems. Earlier in life, she suffered a stroke that left her with one a functional eye and a glass replica in the other socket. Only a few layers underneath her prickly exterior was a person contextualized by life.

In “The Metal Clan,” the upswing of a new Book 3 arc, Korra is the blissfully ignorant student, learning the facts for the first time. We've known Lin Bei Fong since the very beginning of the show, but we've never known her. And a thinner show would have been OK with that; Lin's the gruff, overly-rational policewoman who will do anything to protect the Avatar from danger. That's enough characterization. But not for 'The Legend of Korra,' which shook up the Korra/Lin relationship by traveling to the heart of the Metalbender's past.

Despite Zaheer and Co. being on the hunt for Team Avatar, Korra leaps at the chance to find another Airbender. They find one in Zhao Fu, home to a utopian society of hippie Earthbenders known as the Metal Clan. Lin wants to part of the headhunting mission; When Asami's airship lands on Zhao Fu grounds, she holes up inside, refusing to leave like she's the grandmother in 'Dante's Peak.' There's no arguing with her, a quick “Why?” met with more growling. No skin off Korra's nose. This is Lin acting more Lin-like than usual. Korra's personal explanation of the behavior: “Just 'cuz.” I'd guess Michael Dante DiMartino, who wrote the episode, has a Lin Beifong too.

Soon, Korra finds herself knee deep in a family feud (and not the good version with Richard Dawson). The mother of the fledgling Airbender is none other than Suyin Beifong, half-sister to Team Avatar's law enforcer. Played with airy poise by Anne Heche, Suyin's the liberal arts-educated, poetry-quoting, world-traveling, 'New Yorker'-reading, self-identified foodie to Lin's blue collar, bread-and-butter townie. When they're finally forced to cross paths, caught in their white lie by Suyin's assistant Wei, who uses Earthbending as a vibration-sensitive lie detector, Lin explodes in a fit of rage. The storm dredges up old baggage: Lin resents her mother (Toph from Avatar: The Last Airbender) for getting with another man and having Suyin. She directs the anger at her half-sister, they're polar opposite paths in life making the divide between them a volcanic crater. The day of this episode is the first time they've spoken in 30 years. Sit on that for a second.

It's hard to completely trust  Suyin. Her life is perfect. Her kids are perfect. The city she helped build is perfect. So was Dome World in 'Logan's Run.' A tip off that she might be up to no good — or that her morals aren't 100 percent aligned with Korra's — is the reappearance of Varrick, everyone's favorite slime ball. Last season's assassination conspirator is now a mogul under Suyin's eye. This is a brilliant call back. Instead of giving Suyin a figurative “twirling mustache” that makes sinsiter activity plausible, DiMartino feeds us the possibility by association. And a funny association, at that.

Hoping that enough time spent in the same location might mend the broken relationship, Korra sets out to teach airbendering to Opal, Suyin's daughter. Even if the character doesn't go on to play a huge role in this season, Opal's already made lasting impact. In 'Legend of Korra's' to encapsulate every type of romantic encounter, Opal offers a casual, comforting side of flirtation. She immediately has eyes for Bolin, but it doesn't take anything away from her pursuit to be a great Airbender. Bolin, on the other, is a total fool. First, Opal isn't his type (worthy of a devastating eye-roll). Then he attempts to win her over with a smooth operator attitude that would make Gaston gag. She finally tells him what's up: Be yourself and maybe, maybe they try out romance. Young men out there, I hope you're taking notes.

Serving of sizable portion of setup, DiMartino balances out this episode with a creepy B-plot. In pursuit of Korra, a freshly-shaved Zaheer infiltrates the Air Temple where Kaya and Tenzin's airbending offspring run boot camp. Henry Rollins' voice work is even more spine-tingling when he's playing “nice,” accentuated by horror movie direction.  A muscled airbender with an “X” scar on his bald dome isn't a red flag for anyone at the temple, so Zaheer goes along his way, snooping around campus and impressing people with his mad air skillz (the second, even brighter red flag). After sneaking into Tenzin's room to lift an amulet inscribed with his favorite quote (The second reference to, "Let go your Earthly tether. Enter the void. Empty, and become wind."), Kaya catches him in the act. The fight that commences is brutal, close quarter combat, giving Kaya her first real spotlight of the series. Worth the wait: It's a multi-layered, multi-weaponized rumble that keeps up with the momentum of Book 3.

“The Metal Clan” ends on one of the hardest dramatic gut punches of the show. Hoping to calm an enraged Lin, Opal opens up to her aunt with loving words. Lin can't hear it. It's salt on the wound. Lin fires back with a “get off my lawn” moment. Korra cuts her back: "You're always going to be a bitter lonely woman." That cracks Lin, left in tears. Woof. The scene adds a new twist to the Book title: “Change.” Both Korra and Lin will have to if they're going to walk away from this one intact.

More From ScreenCrush