Season four kicks off in the City of Lights Paris! Blair has spent a fabulous summer in Paris without realizing Chuck, her former love, has been shot. Yet as much as Blair tries to distract herself from the pain Chuck caused her by sleeping with Jenny Humphrey, his mysterious appearance in Paris with a beautiful new woman will force both of them to face what happened. Serena has been enjoying a Parisian summer of love with boys, Blair and Balenciaga as she tries to avoid the inevitable decision about which of her two longtime beaus, Dan or Nate, she should return to. Meanwhile, back on the Upper East Side of Manhattan, Nate meets an intriguing girl, Juliet, who helps him realize that his summer of sexual conquests was his way of avoiding his unresolved feelings for Serena. Plus, Dan's baby mama drama continues with Georgina and the van der Woodsen apartment is buzzing with activity as a "Fashion's Night Out" event is planned.

Living out a real-life fairytale in Paris, Blair is pursued by a handsome young man, Louis (guest star HUGO BECKER), whom Blair suspects is a member of Monaco's royal family. A very concerned Lily asks Serena to help her find Chuck, who hasn't been heard from or seen in months. Meanwhile, Chuck Bass is as we've never seen him before, adjusting to a fresh start in Paris with a mysterious new woman, Eva (recurring guest star CLÉMENCE POÉSY), at his side. And Juliet (recurring guest star KATIE CASSIDY) offers to help Nate win Serena back, suggesting that by reigniting the romance between Dan and Vanessa, it may remove Dan from the Dan-Serena-Nate love triangle.

It's back to the Upper East Side! On her first day at Columbia, Blair attempts to gain membership into an ultra-exclusive social club, Hamilton House, but she's in for a few big surprises. Serena begins to suspect that her life is being intentionally sabotaged by Juliet (recurring guest star KATIE CASSIDY), and that it may have something to do with Nate. Meanwhile, Rufus is worried about Dan and decides to take matters into his own hands.

Nate suspects that Juliet (recurring guest star KATIE CASSIDY) is keeping a big secret from him and decides to confront her. Blair schemes to undermine Chuck's newfound happiness. Dan finds himself torn between his feelings for Serena and Vanessa.

An anonymous Gossip Girl blast starts a very damaging rumor about one of Columbia's new students, Serena. On her path to greatness, Blair decides to take a class with a powerful businesswoman, Martha (guest star MARLYNE BARRETT Damages, Kings, The Wire), who is a guest lecturer at Columbia, but a mysterious fellow student thwarts her plans to secure the prized position as Martha's assistant.

Although Blair made it perfectly clear that Little J was no longer welcome in Manhattan after what happened with Chuck, Jenny is tempted by a once-in-a-lifetime opportunity to meet Tim Gunn (guest star TIM GUNN Project Runway), which could be a game changer for her future. Meanwhile, Serena discovers something about her new boyfriend, Colin (guest star SAM PAGE Mad Men, Desperate Housewives, Shark), that may put an end to their relationship just as it was getting good.

Blair is caught off-guard and not in a good way by a surprise guest at her birthday party. Having had enough of Chuck and Blair's games, Serena and Nate decide to plan an intervention. Musical guest ROBYN performs.

Chuck and Blair decide it's in both of their best interests to put the past behind them and end their vindictive games. Nate confronts Juliet (recurring guest star KATIE CASSIDY) after discovering a secret she has been keeping from everyone. Dan and Nate realize they both still have feelings for Serena.

Chuck hosts a "Saints and Sinners" masquerade party at the Empire Hotel. At the party, Dan and Nate don't know what to make of Serena's strange behavior and mixed messages. Blair sets her sights on becoming the new face of Anne Archibald's (recurring guest star FRANCIE SWIFT The Good Wife) foundation for girls, but Anne is concerned that Blair's friendship with Chuck Bass may be problematic. Recurring guest star KATIE CASSIDY appears as Juliet.

Chuck, Serena, Blair, Dan, Jenny and Eric (recurring guest star CONNOR PAOLO) find themselves faced with a crisis when a member of one of their families is hospitalized. Meanwhile, Nate attempts to help his parents, the Captain (recurring guest star SAM ROBARDS) and Anne (recurring guest star FRANCIE SWIFT), put their complicated past behind them and reconcile. Recurring guest star KATIE CASSIDY appears as Juliet.