It's Heidi's 21st birthday, so Spencer sends a big bouquet of roses to her office. He's excited to celebrate his fiancée's big day, saying in the card that Heidi's "the greatest thing that ever happened" to him.But that's not the only big event that's taking place. After weeks of hard work, the Teen Vogue Young Hollywood party that Whitney and Lauren helped put together is finally here. Editor Lisa Love tells Lauren that she'll be backstage with the models while Whitney works the front of house, which Lisa says will be "horrible" and "chaotic." Despite knowing it's going to be a madhouse, Lisa is adamant that there should be no "screw ups" and the Marc by Marc Jacobs fashion show must start on time.During her lunch break, Audrina tells an Epic Records co-worker that she and Justin are going to check out The Ruse, an unsigned band, that night. Audrina wants to scope them out for Epic ... and spend some alone time with Justin, even though she's not quite sure it's date.Meanwhile, during Heidi's birthday lunch with new Bolthouse employee Kimberly, Heidi orders a glass of wine to celebrate the fact that she's finally legal. It's been a big year for Heidi, who says she feels like she's experienced a lot of personal growth. Heidi says she's not going to get wild and crazy on her birthday; she's just going to have a low-key dinner with Spencer since he's all that really matters in her life. Kimberley's surprised that Heidi doesn't want to have a big blowout to celebrate her 21st, which only happens once in a lifetime.While preparing for the Teen Vogue Young Hollywood party, Lauren and Whitney are tasked with putting together 1,500 gift baskets. They discuss the fact that Whitney's in charge of seating, and she admits she's worried that she might be in over her head. She knows her biggest priority is getting everyone seated on time.A few hours later, Whitney's briefed on what's going to go down that night and learns that she must seat close to 400 people in just fifteen minutes ... and there's no seating plan. Whitney will be the point person for the event, which means she'll have to take the blame if something goes wrong.Backstage, Whitney and Lauren test their headsets and run through their communication channels to make sure everything works and they know exactly what they're doing. As Lauren starts dressing the models and Whitney gets ready to seat people, Teen Vogue editor Lisa Love scopes out the red carpet, which is getting backed up and leaving celebrities like Hayden Panettiere standing outside. With all the red carpet chaos, she decides the fashion show must be pushed back 30 minutes.Meanwhile, Audrina and Justin hit the Viper Room to watch The Ruse. After the show, Audrina introduces herself to the band, mentioning that she works for Epic Records and plans on giving their CD to the label's A&R rep. After chatting it up, the group invites her and Justin to an after-party.Elsewhere, Heidi is celebrating her birthday with Spencer, who presents her with the newest, biggest Chanel bag on the market. Heidi squeals with delight, saying it's the best gift ever. But when the conversation cools, Heidi puts on a glum face, leading Spencer to ask what's wrong. She says she's fine, but could Heidi be bummed she didn't opt for a big party?Back at the Young Hollywood party, things are really heating up. Whitney frantically starts seating guests as Lauren tries to touch base with her via the headset. When Whitney doesn't answer, Lauren seeks her out and discovers that she has removed her earpiece.With everyone seemingly seated, Whitney tells Lauren everything is good to go, so Lauren runs backstage to tell the models to head out onto the runway. But as soon as Lauren disappears, Whitney discovers that Hilary Duff hasn't been seated yet. The show can't start until Hilary is front and center, but Whitney can't seem to get in touch with Lauren! As the models ramp up, Whitney finally gets Lauren on the line and Hilary makes it to her seat just as the fashion show kicks off.While having drinks with The Ruse, Audrina orders a "Naughty Schoolgirl," which comes with a lollipop. When Justin slips off to the bathroom, one of the band members slips in and starts chatting up Audrina, inviting her to an after-after-party. But when Justin returns, the guy wonders whether Audrina is spoken for.When Audrina steps away, the band member that has his eye on her approaches Justin to find out what their deal is. Justin tells him they're "cool." But when the dude asks if he can ask Audrina out, Justin clicks his tongue, shakes his head and says she's already "pretty good." When Audrina comes back, Justin says he thinks it's time to leave. While walking out the door, Justin teases her about the guy from The Ruse and they share a laugh.Back at the Young Hollywood party, the festivities are in full swing and go off without a hitch. Afterwards, Whitney and Lauren get the thumbs up from Lisa Love and Teen Vogue editor in chief Amy Astley, who applaud them for their good work and suggest they do this type of party every year.Finishing up her 21st birthday bash with Spencer, Heidi says she's happy to have a drama-free celebration. But while she silently eats a slice of cake while Spencer texts someone, Heidi doesn't look too happy.