Lauren, Heidi, Audrina and Whitney face new challenges at work and school as well as in the romance department.

Lauren works a swimsuit fashion show; Heidi's pregnancy test is negative, but she lets Spencer sweat it out a bit.

It's Heidi's birthday, and Audrina is not invited to the party, but she shows up anyway.

Heidi is skeptical when Audrina tells her Spencer is a cheater. Meanwhile, Lauren wonders if she is ready for a relationship.

At Teen Vogue, Lisa Love tells her interns that there's a dinner party to plan, and the New York intern, Emily, will be flying over to help. Meanwhile, at Bolthouse, Heidi takes a phone call from Spencer. When he asks why she hasn't returned his calls, Heidi reminds him about the night before and tells Spence she needs a week to clear her head.

Lauren tells Heidi what she really thinks about Spencer, and Heidi has to choose between her best friend and her boyfriend.

At the club, Spence tells Jen that he brought Brody as her birthday present. Jen keeps asking Heidi if the hookup will hurt Lauren, but Heidi tells her friend to do what she wants on her birthday. Thinking Brody might not be the best idea, Jen tells him he might want to leave her side, and Brody says he doesn't want to deal with drama.

Whitney is becoming fed up with intern work; Heidi and Spencer take a trip to Santa Barbara; and Lauren goes on a double date with Audrina. Also: Lauren's miffed when Heidi bails on plans and hangs with Spencer instead.

Spencer invites Heidi to move in with him, and she doesn't know how to react.

Audrina and Heidi throw a party for Lauren's 21st birthday that's full of surprises, and Jen tries to apologize to Lauren.

Spencer gets into a heated conversation with Heidi at his favorite restaurant, Don Antonio's. Bringing up his move-in proposal yet again, he can't quite understand why Heidi isn't ready to take the plunge. He's nonplussed when Heidi questions his loyalty, saying there can't be a repeat performance of the playboy incident.

Spencer finally persuades Heidi to move in with him, and Lauren has to find a new roommate. Meanwhile, Whitney heads to New York to interview for a full-time position with Teen Vogue.