In a fashionable farewell to remember, our favorite Upper East Siders join forces for one last soiree, and the shocking identity of Gossip Girl is finally revealed.

Blair and Dan join forces to find Juliet. Serena expounds her boarding school experiences to her therapist and discovers the truth behind Juliet's vendetta against her. Meanwhile Chuck suspects Lily has not told him the full truth.

The Constance Billard and St. Jude seniors have the production of "The Age of Innocence". Serena has a crush on the play's director, Julian, and enlists Vanessa's knowledge of theater to help her get the guy's attention. Blair receives bad news about her future that leads her on a witch hunt for the person responsible. Dan and Rachel agree to stay away from each other in the aftermath of being discovered as more than teacher and student, but find it impossible to keep that promise. Chuck find help on an unlikely friend, Carter Baizen.

In a flashback to the 80s, 17-year-old Lily Rhodes gets kicked out of boarding school and runs away to Los Angeles, reconnecting with her parents, Rick and Cece, and sister, Carol. Back in present day, Blair and Nate attend prom together, but the evening doesn't turn out exactly as planned and Chuck and Serena have a little something to do with that. Serena and Lily don't see eye-to-eye over Serena's recent run-in with the law.

"It girl" Serena van der Woodsen has returned to Manhattan after a mysterious and self-imposed exile to boarding school. Serena's best friend, Blair Waldorf, has conflicted feelings about her friend's return since she has enjoyed being the Queen Bee during Serena's absence and might not be ready to relinquish her new position on the social ladder, not to mention the fact that she has always suspected there may be unspoken feelings between Serena and her longtime boyfriend, Nate.

The entire Upper East Side of Manhattan is rocked when Bart Bass dies suddenly in a limo accident. Serena and Eric take the news very calmly while Lily has a troubling time despite her mother, Cece's, awkward attempts to comfort her. Chuck begins to blame Lily for his father's death and threatens to reveal a secret that Bart found on her before his accident. Meanwhile, Blair's mother, Eleanor, prepares for her latest marriage to Aaron's father Cyrus.

Chuck and Blair decide it’s in both their best interests to put the past behind them and end their vindictive games. Nate confronts Juliet 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 foundation for girls, but Anne is concerned that Blair's friendship with Chuck Bass may be problematic.

The episode continues from the early events of the Constance Alumni event. Georgina Sparks turns up at the event looking for trouble. Serena and Vanessa reluctantly join forces to find Dan and Charlie, who does not take Dan's rejection of her well. Blair must make a choice between the men in her life when her life is in danger by Russell.

Gossip Girl reports that Serena van der Woodsen was seen buying pregnancy tests. Of course, on the Upper East Side, the truth is often even juicier and more scandalous than the gossip. Nate finds out about Blair and Chuck's affair. And when everyone else finds out what happened Blair's life comes crashing down. Meanwhile, Dan struggles to tell Serena those three special words.

Lily and Rufus decide to move up their wedding to the next day, but will someone or something come between them before they become man and wife? Chuck discovers a secret that Carter has been keeping from Serena. Dan and Vanessa are pulled into one of Georgina’s schemes. Blair is suspect of Bree and shares her concerns with Nate.

It's Ivy week for the Upper East Side teens of Constance Billiard and St. Jude's and the visiting representatives' arrival brings more than just college applications. Cut-throat rivalry is at its sharpest this week as the students compete for prestigious positions. Blair discovers a shocking but juicy secret about Serena and plots to drop the bomb at the best possible moment. Dan is sure that landing the coveted usher position with the Dartmouth rep will either make or break his future at the school. Unfortunately, it's Nate who nabs the position, despite total disinterest in the school. Meanwhile, Jenny gets closer to Serena's younger brother Eric and Rufus asks Lily for a favor.

Vanessa uses the scandalous picture of Catherine and Marcus to blackmail Blair into being a nicer person, so Blair seeks revenge by enticing Chuck to seduce Vanessa. Lily and Bart throw an extravagant housewarming party and expect their children to make them proud in front of the attending press, but a rebellious Serena isn't ready to play by their rules. Meanwhile, Dan and Jenny discover a big secret that Nate has been keeping from his friends.

It's Thanksgiving time and Blair is offended when her Mom's new man hijacks her Thanksgiving traditions. Lily attempts to strengthen the frail bond between Rufus and Jenny. Eric discovers a secret about Bart. Vanessa and Chuck help Nate deal with his father.

Gossip Girl decides to liven things up at the Constance Billard and St. Jude’s graduation by sending out a shocking and damaging email blast in the midst of the commencement ceremony, stirring Serena to come up with a plan of attack. The Mean Girls challenge Jenny to throw her hat in the ring to succeed Blair as Queen Bee next year. Lily and Rufus struggle to repair their relationship after Lily’s betrayal. As for the cliffhangers, Blair and Chuck finally… and Serena is shocked by… and Georgina decides to… and Dan, Nate, and Vanessa unknowingly…. Jenny and Eric do something they might end up regretting.

Chuck offers to throw a wedding for a very pregnant Dorota who insists that she and Vanya have a traditional wedding before her parents arrive from Poland and find their daughter pregnant and without a husband.. Dorota asks Blair and Chuck to be part of the ceremony and walk her down the aisle. Serena tells Nate she is having breakfast with the Humphreys when in reality she’s secretly meeting up with Carter Baizen. Rufus discovers that Lily has been lying to him about her whereabouts.

A former associate of Chuck’s father, Russell Thorpe – along with his daughter Raina – returns to Manhattan with some unfinished business for our Upper East Siders. Serena and Chuck join forces against Lily. Blair realizes that her mother, Eleanor, may be her key to becoming a future CEO. Nate worries that his father, The Captain, is having a little too much fun and not taking his parole seriously.

It wouldn’t be a proper Upper East Side party without some major Gossip Girl drama, and for Eric’s 18th birthday celebration there is plenty to go around. Blair decides to speed up the time table on her career path to becoming a powerful woman.... but ultimately stretches herself too thin. Serena is forced to choose between her family and Ben. Chuck and Lily’s relationship remains icy in the aftermath of Lily’s betrayal.

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.

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.

Blair gets excited when her mother, Eleanor, chooses her to be the new face of her clothing line. However, Blair's happiness turns quickly into feelings of betrayal and jealousy when Serena takes her spotlight and Blair finds herself back in Serena's shadow. Meanwhile, Serena and Dan remember once again that they come from two very different worlds. Also, Nate and Chuck do a boys weekend to blow off steam after Ivy Week ends.

It's their first official date and Dan tries to impress Serena with an elaborate plan for the date, but fails to understand that Serena is happier with beer than champagne. That same night Jenny is invited to the infamous Blair Waldorf sleepover and finds herself in a high stakes game of "Truth or Dare". Meanwhile, Lily finds out that Erik is missing from the treatment center, and she finds herself seeking help from her ex-boyfriend, Rufus.

Serena's world descends into chaos when a former friend, the evil Georgina Sparks returns to town. Nate connects with the last person he expected, Vanessa. Blair hatches a plan to sabotage her biggest rival, Nelly Yuki. Meanwhile Serena goes out with Georgina, but things get so bad that Serena thinks someone spiked her non-alcoholic drink. Jenny develops a crush on a dog-walker, Asher Hornsby, who might be her ticket to permanent popularity.

After Georgina reveals the true reason Serena left Manhattan, Serena goes back into her old habits. Her friends Blair, Nate, and Chuck, in order to help her, have to put their differences aside. Meanwhile, Rufus is excited when his band is invited to perform at a Rolling Stone-sponsored concert, but Lily is the last person on earth he expects to see at the performance, especially since her wedding rehearsal dinner is the same night.

Blair takes matters into her own hands to help Serena with the manipulative and evil Georgina Sparks. Lily, while keeping Rufus in her mind, prepares for her wedding with Bart Bass that is designed to be the Upper East Side's social event of the year. Serena finally tells Dan the whole truth about her past and they try to work things out after Dan has cheated on her, but will it be too late? An unexpected guest shows up at Lily and Bart's wedding. Georgina is sent somewhere where she can do no harm. Blair plans to go somewhere with Chuck.