A very complimentary Brittany approaches Kurt at his locker with a proposition: she wants to run his campaign for class president, because he's the school's biggest "unicorn" (in Brittany-speak, a unicorn is someone who knows they're magical and isn't afraid to show how special they are). She feels that her popularity - and the fact she's slept with a lot of people - should help bring him votes, and Kurt agrees to let her manage his election bid.
Will informs the glee club that because of Vocal Adrenaline's second-place finish at Nationals, coach Dustin Goolsby is out and a replacement for the high-pressure position has been difficult to find, leaving that team vulnerable. To take the edge, Will won't be directing the school musical, and he institutes a mandatory "Booty Camp" coached by Mike after school for the students who need serious help perfecting their dance moves: Finn, Puck, Kurt, and Mercedes, plus volunteer participant Blaine. Will also unveils the school musical's new co-directors, Emma and Coach Beiste, along with the initially reluctant student director Artie.
Will's old flame - and Rachel's birth mother - Shelby Corcoran surprises him in the teacher's lounge. She's a new part-time instructor at McKinley after being hired to start a second show choir featuring Sugar Motta, funded by a donation from Sugar's father. Will worries about what Shelby's presence will mean to Rachel - as well as to Puck and Quinn, whose baby, Beth, was adopted by Shelby. Shelby says that she plans to use her time in Lima to correct the mistakes she's made. After she promises not to poach from New Directions, Will welcomes the competition her second glee club will bring as it bolsters arts education at McKinley.
After Quinn and her new girl gang, The Skanks, shake down a student for her lunch money, Sue requests some time to talk to Quinn: she blames all of Quinn's losses on her involvement in the glee club and offers her a chance for both revenge and stardom. Sue wants Quinn to star in a video for her anti-arts Congressional campaign as "a girl from whom the arts stole everything." Quinn seals the deal with her.
Brittany's campaign plan, posters, and goodies come off as too gay-centric for Kurt (including a planned swag bag called "Kurt Hummell's Bulging Pink Fun Sack"). Kurt unveils his own spin, inspired by Judy Garland and which is, in Brittany's estimation, "so unicorn."
Quinn and Puck meet with Shelby, who believes that they might want to have a presence in their daughter's life. Quinn initially rejects the idea, and Shelby tries to persuade her. But Shelby also insists that Quinn clean up her act before she sees Beth, because Quinn is the only real mother Beth has and Shelby will never be able to fulfill that role.
While Will and Mike run their Booty Camp students through their dance paces, Blaine reveals that he's planning to audition for "West Side Story's" Tony, the role Kurt had also targeted, though he thinks it'll probably go to Kurt because he's a senior.
Shelby approaches Rachel as she works through vocal exercises to prep for the musical audition, and though Rachel is initially resistant to having contact with her birth mother, Shelby persists. Shelby suggests that Rachel sing "Somewhere There's a Place for Us" - as a veteran of 18 stints as Maria, she thinks it's the song that will put Rachel over the top - whereas if Rachel plays it safe with "I Feel Pretty," she'll never get the part or be a star. Rachel tries the song, with Shelby joining in and adding an extra layer of meaning as they duet.
As part of Sue's campaign film, Quinn confronts Will on-camera, telling him that glee club robbed her of everything and that she'll never come back. Sue's delighted with the scene as it's playing out, but Will tells Quinn that the only person she cares about is herself - she's no longer a girl, and she shouldn't continue to play the victim card. He reminds her that the glee club was there for her at every turn without so much as a thank you, and he rejects the blame she lays on his shoulders by telling her to grow up.
Puck shows up at Shelby's home unannounced, hoping to prove that he's trying to clean up his act. Though impressed, Shelby reminds him that his efforts can't be a sprint - they need to be a marathon. Puck is clearly moved when he gets his first glimpse of Beth, and though he's too nervous to hold her, he promises to do anything to prove himself worthy of being in Beth's life.
Later, Puck urges Quinn to follow his lead and shape up her attitude, but she insists that they're not parent material and that they'll never be together, only to be surprised by Puck's adamant stance: he doesn't care about Quinn, he cares about Beth. He says that he doesn't want her having unanswered questions that will screw her up later, and he believes that Quinn has to be a part of Beth's life.
Emma, Artie, and Coach Beiste get their first look at the "West Side Story" hopefuls, beginning with Kurt's dynamic audition with the "seminal and in my case semi-autobiographical" song "I Am the Greatest Star" from "Funny Girl," complete with a scaffolding (and written permission from Rachel to sing a Barbra Streisand staple). Kurt then eavesdrops on the directors, who have narrowed the early Maria contenders down to Rachel and Mercedes, but quibble over the Tony casting: while they agree that Kurt owned his song "like it was his prison bitch," Coach Beiste argues that Tony needs an alpha dog, "street" quality that "excites her lady parts." Artie agrees that Kurt may be too delicate to convincingly play the role.
Adding to Kurt's concern over potentially losing the part is his horror in discovering that Brittany's papered the McKinley halls with her pink, rainbow, and unicorn-centric campaign posters for Kurt ("The poster that you wanted gave me crippling depression," Brittany explains). Grabbing Rachel to help him in an emergency second audition, Kurt insists that Brittany scrap the campaign posters and leaves her feeling like she's failed her "precious unicorn." But Santana tells Brittany that her campaign plan was genius and that she, in fact, is a unicorn, too.
Attempting to convince the directors of the romantic masculinity he can bring to the part of Tony, Kurt re-auditions with a scene from the inspiration for "West Side Story," William Shakespeare's "Romeo and Juliet." When his performance draws suppressed giggles from not just the judges but also from his scene partner, Kurt storms off the stage.
After beginning her training of the perpetually off-key Sugar Motta, Shelby explains to Quinn that she, too, followed a rebellious, painful path after she gave up her own baby for adoption, but she eventually came to realize that she had done right by Rachel. Quinn insists that she'll never go back to being the blonde, perfect girl she used to be. Shelby suggests that Quinn was never that girl to begin with - would that girl have gotten pregnant in the first place? Shelby urges Quinn to find herself and stop punishing herself for the mistakes she made as a child.
Quinn asks to see Beth, but Shelby says it's too soon. Quinn begs to at least see a photo of her daughter, and Shelby shows her a camera shot of Beth and Puck, telling a tearful Quinn that she can still be a part of the family she sees - it's all up to her.
While Rachel frets over the casting outcomes despite the seeming inevitability of her claiming the Maria part, she tells Finn that the Tony field remains wide open. But Finn says that between school, football, and especially Booty Camp he can't fit it in. Rachel doesn't want to see Finn pass up opportunities to show his talent, and she suggests that he might even be talented enough to get into the New York Academy of Dramatic Arts, where she hopes to go.
For the first time, Finn tells her that one option might be staying in Lima and working for his stepfather. Rachel thinks that path's fine if it will make Finn happy, but she doesn't think it will: even if he doesn't think he's fit for something better, she believes in him.
As Kurt sulks over his prospects in the musical, his dad, Burt, talks to him: he points out that Kurt's gay and obviously, unabashedly so, and what's wrong with that? Kurt says while he's not ashamed of who he is, he wants his shot at the great musical romantic leads and is hurt not to be seriously considered for straight parts. But Burt suggests that if roles suited to Kurt don't exist, he needs to change the game and create them himself. When Kurt chafes at being a "unicorn," Burt reminds him: "Do you know what they call a unicorn without a horn? A freakin' horse."
At Booty Camp, Finn stumbles on a routine and grows frustrated, insisting that he can't master the steps, but Will tells him he believes in him. Finn gives it one more shot and nails it.
Unexpectedly, Quinn arrives at the dance class - her hair back to blonde, the nose ring gone, and the Goth clothing done away with - and asks to join in the training session. Will and the glee club welcome her back, and Puck tells her that he's proud of her - but Quinn quietly tells him that she wants them to get full custody of Beth and she'll do anything to achieve it, including pretending to be someone she's not.
When Will tells a cocky Sue that Quinn's return has invalidated her campaign video, Sue insists that it's even better now: Quinn's shown herself as an addict who's returned to the empty promise of performing dreams. Sue also informs them that her popularity is surging, and she's just taken over the first place spot in the election polls. Will, Emma, and Beiste plot to find a credible contender to challenge her - "the anti-Sue," as Beiste puts it.
Brittany is thrilled when she discovers Kurt re-hanging her unicorn-themed campaign posters in the halls, having embraced his uniqueness. But when Kurt invites her to help him strategize his next move, he discovers that Brittany's meeting with Santana to plot out her own campaign for class president: "I'm also a unicorn - or maybe a bi-corn - and I'm starting to believe in my own magic."
Blaine appears before the musical directors to audition, dazzling them with his performance of "Something's Coming," another "West Side Story" staple. While Blaine was only intending to go for the roles of either Bernardo or Officer Krupke, his performance moves Artie to suggest that he read for Tony, leading to a tense moment of indecision for Blaine and major pangs of hurt and jealously for Kurt.