Serena loves her new job in Hollywood, but makes a costly misstep when she tries to impress her boss. Chuck and Nate arrive in Los Angeles as the last stop of their Lost Summer trip, joining Serena at a glamorous Hollywood Hills party, where Nate meets a sexy older woman. Blair and Louis return from Monaco and begin planning their royal wedding, but when Louis refuses to stand up to his family and support Blair's choices, his weakness threatens their relationship. A magazine is planning to run an excerpt of Dan's book until an unlikely ally steps in to help himhug the story.

Nate reconnects unexpectedly with Diana, who offers him an exciting opportunity. Serena forces Charlie to decide which world she wants to embrace. Dan seeks out Chuck's help to stop the publication of his book, but discovers it is Chuck who needs the help. Blair's future sister-in-law, Beatrice, arrives from Monaco, but her motives with Blair may be more than just to get acquainted.

Nate must decide whether to cross moral lines at Diana's request. Dan has figured out who is publishing his book, and seeks help to stop it, but he ends up in the spotlight anyway. Chuck helps Dan come to terms with his fate, just as Dan continues to try to help Chuck break through his emotional block. Serena and Charlie return to the Upper East Side from California.

After much deliberation, Dan decides to gather Serena, Blair, Nate, Chuck, Rufus and Lily to reveal the truth about his book in the hope that they will support him at his book party. Meanwhile, Blair and Louis hit a crises point after Louis reads Dan's book. Diana learns incriminating information about one of Nate's friends and uses it to her advantage.

In the midst of celebrating Yom Kippur with family and friends, Blair and Louis find themselves in a power struggle with Louis' family. Serena's boss puts Serena in the awkward position of choosing between her new job and her relationship with Dan. Diana prepares to debut the New York Spectator, but an unfortunate last-minute surprise delays the launch and Diana expects Nate to do whatever it takes to save the day.

Blair makes all of her former minions and Charlie compete to secure the coveted bridesmaid spots in her upcoming royal wedding. Nate is tired of keeping his relationship with Diana a secret, so he decides to use Charlie to make Diana jealous. Serena's boss is determined to acquire the film rights to Dan's book, so Serena must put her personal feelings about Dan and the book aside in order to close the deal.

Several of our favorite Upper East Siders attend a performance of Punchdrunk's provocative theater experience, "Sleep No More", which translates to masks, anonymity and some surprising romantic twists by the end of the evening. Meanwhile, Diana sets her sights on Serena in her quest to ruin Gossip Girl. Dan is out on his book tour, but things aren't exactly as they appear to his friends and family.

Serena is hard at work planning a dream bridal shower for Blair, but it should come as no surprise that Serena has to plant some false information about the shower in order to keep Blair from finding out all the details. Chuck and Dan decide to spend the day together to distract themselves from the fact that they didn't make the invite list for Blair's shower. Nate and Serena find a silver bullet in Diana's war against Gossip Girl, but struggle about whether to use it or not.

Lily, Charlie and Serena eagerly anticipate the Studio 54 party being thrown in CeCe's honor. Nate takes on a new role at the Spectator, but his first big story turns out to be about someone he knows all too well. Blair turns to an unlikely person for help.

Lily throws Charlie a party to officially introduce her to New York society. Meanwhile, Charlie's ex-boyfriend, Max, throws a wrench into Charlie's future as an Upper East Side princess. Dan decides it may be time to tell Blair the truth about his feelings for her. Chace Crawford, Ed Westwick and Matthew Settle also star.

Blair's flashbacks reveal the fallout of her and Chuck's car accident, which Nate realizes may have been caused by foul play. Meanwhile, Lily gets a private eye to locate Charlie; and Vera Wang makes an appearance at Blair's bridal-dress fitting.

Blair prepares to celebrate her upcoming royal wedding with a bachelorette party, but others scheme behind her back to make this a night to remember. After discovering the truth behind Chuck and Blair's car accident, Nate joins forces with a surprising ally to gather the evidence. Serena and Dan pretend to be dating again to protect someone close to them.

The much-anticipated 100th episode will open with a musical dream sequence featuring Serena, Blair and all the men in their lives. Also, while Chuck wrestles with the reality that Blair is about to walk down the aisle with Prince Louis, the return of Georgina Sparks might make the royal affair a royal disaster.

Blair must make a difficult decision about her future, the consequences of which could hurt those she loves most. Serena takes the blame for an incident with Gossip Girl in order to protect someone she loves. Georgina smells the scent of scandal and decides to follow its trail.

It's Valentine's Day on the Upper East Side and Blair can't resist playing cupid for someone she loves. Georgina is intent on stirring up more drama, so she decides to crash Nate's Valentine's Day party. Meanwhile, Serena is shocked by something she witnesses at the party.

Dan feels honored when he learns that Upright Citizen's Brigade is performing excerpts from his book, Inside. Blair tries to prove Serena's suspicions wrong in order to save their friendship. On her way out of town, Ivy ends up on a collision course with the van der Woodsens.

Blair thinks Cyrus may have found a potential loophole in her prenup. Chuck and Georgina partner up in a scheme, but it has an unpredictable outcome. Meanwhile, a family crisis brings William van der Woodsen back to the Upper East Side.

Chuck invites Jack to town to thank him for saving his life, but finds the trip doesn't go exactly as planned. Blair and Dan attempt to consummate their new relationship - but unexpected roadblocks get in their way. Meanwhile, Ivy finds an unlikely ally in William in her quest to be accepted on the Upper East Side, and Nate is hopeful a new investor will save his newspaper.

Serena decides she is ready to relinquish the spotlight and sets out to make a reluctant Lola the next "It Girl" of the Upper East Side, starting with modeling at a Kiki de Montparnasse lingerie show. Meanwhile, Chuck reaches out to Blair for advice about his past, and Diana Payne's return to The Spectator starts a power struggle with Nate.

To celebrate their official coming out as a couple, Blair and Dan host a glamorous British-themed Salon, including guests Julian Tepper and Jenna Gribbon (founders of The Oracle Club). Lola lands the audition of a lifetime, but Gossip Girl may have other plans for the Upper East Side's latest It Girl. Meanwhile, Lily and Rufus disagree over the best way to handle the Ivy situation, and Serena and Diana face-off over secrets they both would prefer remain secrets.

Blair feels like her Upper East Side status might be slipping away and devises a plan to assure that doesn't happen. Meanwhile, Lily throws a family gathering - including William, Carol and Lola - in an attempt to prove the van der Woodsen family is as united as ever. Finally, Nate digs into Diana's past and is surprised by what he discovers.

Chuck, Nate, Blair, Serena and Lola team up to uncover what they think is an explosive secret between Diana and Jack. Meanwhile, Dan is offered a prestigious fellowship in Rome for the summer.

Blair enlists Serena to be her stand-in at an important meeting when Blair finds herself needing to be in two places at the same time. Meanwhile, Ivy and Lola team up to help Chuck with a personal vendetta, and Nate makes a decision about the future with Diana Payne.

When Gossip Girl goes after Blair as she's never done before, Serena admits she may have unintentionally played an important role in Blair's latest nightmare. Meanwhile, Nate invites Lola to move in with him, and Lily must make a big decision about the future of her marriage. Finally, by episode's end, Blair will make a choice between the two men in her life... will it be Chuck or will it be Dan?.