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.

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.

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.

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.

Blair must decide whether to meet Chuck at the top of the Empire State Building or risk losing their future together. A Gossip Girl gossip bomb involving Dan explodes Serena and Nate's relationship. Dorota and Vanya welcome their baby. Jenny hits rock bottom. Georgina returns to the Upper East Side...and she has an agenda.

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.

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.

Serena and Dan finally accept that they are crazy about each other, despite that they come from polar opposite worlds. Chuck thinks of investing in a club trying to make his father Bart Bass proud of him. Nate confronts his father, about the drugs he found in his house but he denies having a problem. Jenny discovers a secret that her parents have been keeping from her. Finally, Blair is devastated by Nate's actions when Jenny reveals that Nate kissed her by accident thinking she was Serena.

Georgina informs Serena that she can reveal a deep dark secret from Serena's past, but no one is prepared for what Georgina does next. Blair and Jenny's power struggle continues when each of them start spreading scandalous rumors about each other on Gossip Girl. Dan sees Jenny's new beau, Asher, cheating on her, but Jenny won't listen to him. Rufus goes to Lily for advice on how to handle Jenny's new behavior. Serena tries to confront Georgina, but she leaves before Serena has a chance. After this, Serena says that she and Georgina are not friends.

Jenny has a new young model friend, named Agnes, who encourages Jenny to explore her wild side, and also to confront Eleanor Waldorf who is planning to steal Jenny's designs in order to pass them off as her own. Meanwhile, Serena and Dan attend Rufus' latest art opening as friends, but then Serena meets an artist, named Aaron Rose, and the evening gets a little uncomfortable for Dan. Elsewhere, Blair attempts to seduce Chuck, but he proves to be tougher than she ever imagined. Also, Jenny begins to have a mutual feelings with Nate as he's staying with her, Dan, and Rufus while searching for a place to live.

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.

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.

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.

After a run-in with an increasingly paranoid Bart, Blair grows alarmingly concerned for Chuck’s safety. However, feeling confident that his father will never hurt him, Chuck makes a deal that could change his life. Wanting to make things better for Chuck, Blair devises a plan with the help of Serena, Georgina and Sage to try and get what they need out of Bart. Meanwhile, Nate's financial dilemma finally lands him in a place that he never thought he would be.

As the summer draws to a close in the Hamptons, Serena and Nate have everyone fooled into thinking they are a couple to cover up the fact that Nate has been hooking up with a married, older woman. Blair returns from abroad with a hot guy on her arm, making a very jealous Chuck question his decision to leave Blair stranded at the heliport. Dan has spent the summer assisting a famous author. While interning for Eleanor Waldorf's company, Jenny sneaks an invite to a much-coveted Hamptons' White Party at which Eric introduces her to socialite Tinsley Mortimer.

Serena invites Aaron to a charity event, but soon uncovers a secret Aaron has been keeping from her. Thinking it will help her get into Yale, Blair agrees to babysit the 15-year-old daughter of a Yale donor, but her plan quickly backfires. Meanwhile, Jenny and Agnes plan a fashion show.

Blair puts pressure on Georgina to making amends for her past bad behavior by helping her in an evil plan. The rivalry between Nate and Chuck over Blair reaches a boiling point. Lily makes a secret plan to help Rufus with Dan's college tuition.

On the anniversary of Bart Bass’ death, Chuck wrestles with an issue from the past and a serious car accident rocks the Upper East Side. Dan and Vanessa attempt to navigate their newly complicated friendship. When Jenny is accused of beating up one of her classmates, Eric is faced with a tough dilemma.

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.

Serena's grandmother announces that Serena has to go to Debutante Ball. However, Dan is not what CeCe wants as an escort for Serena, and she makes her opinion heard loud and clear, causing a rift between Serena and Dan. Although they are officially broken up, Nate asks Blair to go to the ball with him. A jealous Nate begins to suspect that Blair is seeing someone else. Jenny finds herself having to make the decision of either attending her mother's art opening or following her dreams to the Debutante Ball, even though her parents don't want her to go.

Having been recently dethroned as Queen Bee, Blair returns to school with the support of Serena to find she is still on the outs with her old friends. Dan visits his mother over spring break, and when he returns, Jenny is on the verge of becoming a full-fledged member of the A-List crowd. Jenny must go to dangerous and even illegal lengths to fit in. Serena struggles to adjust to living with Chuck, and receives disturbing packages from an unknown sender.

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.

In the midst of Fashion Week, a furious Blair learns that her mother, Eleanor, at the suggestion of her protege Jenny, has given Serena and her new socialite friend, Poppy Lifton, front row seats to the Eleanor Waldorf show. Hurt once again by Serena's popularity and her mother's betrayal, Blair decides to sabotage the show. Meanwhile, Dan starts hanging out with Chuck, but a walk on the dark side always has its risks and Dan learns that the hard way. Lily learns a secret that her new husband, Bart, has been keeping from her.