The privileged prep school teens learn that Serena van der Woodsen is back in town.

In the wake of the scandalous Kiss on the Lips party, Serena receives an icy cold reception from Blair.

Blair uncovers scandalous information about Serena; Dan sets his sights on impressing the Dartmouth representative.

Blair is thrilled when her mother, Eleanor, chooses her to be the new face of her clothing line; Serena and Dan are reminded once again that they come from two very different worlds; Nate and Chuck indulge in a boys' weekend to blow off steam after Ivy Week.

Dan makes elaborate plans to impress Serena on their first official date; Jenny is invited to the infamous Blair Waldorf sleepover and finds herself in a high-stakes game of truth or dare; Lily discovers Eric missing from his treatment center, and seeks help from her ex-boyfriend, Rufus.

Dan is torn between two girls when his childhood friend Vanessa returns home and declares her feelings for him

Serena and Dan finally acknowledge they are crazy about each other; Jenny discovers a secret about her parents; Blair is once again devastated by Nate's actions.

Blair puts on a happy face for her 17th birthday party and attempts to hide the truth from her friends.

As 'Gossip Girl' posts news of the annual Cotillion Ball to take place on the approaching weekend, Blair decides not to go with Nate, but she finds herself being featured in The New York Times and is enjoying her secret affair with Chuck. Serena decides not to go either, so her grandmother, CeCe, shows up to change her mind. Meanwhile, Jenny volunteers for the ball and Lily takes her under her wing. But the night of The Cotillion is the night of Alison's first art opening, and Rufus and Alison tell Jenny that she cannot attend the ball. Jenny decides to defy them both by secretly attending the dance anyway. Refreshed by Blair's newly buoyant attitude, Nate asks her to the Cotillion and she accepts, which makes Chuck jealous. CeCe tells Lily and Serena that she is sick with lung cancer and her last dying wish is to see Serena go to the ball, and she wants Serena to go with the wealthy Carter Baizen. The snobbish CeCe takes an instant dislike to Dan and she approaches Rufus with an offer pay him to convince Dan not to go with Serena. Dan learns of this and tells Serena that he does not think very highly of CeCe by telling Serena about how CeCe tried to bribe his father to persuade him not to attend. Surprisingly, the skeptic Serena refuses to believe Dan that her compassionate grandmother is a crafty snob, and she ends up going to the ball with Carter... both her and Dan having fallen right into CeCe's ploy. Also, Chuck manipulates Nate into thinking Carter is having an affair with Blair to provoke a fight with him.

The gang breaks into the school swimming pool, but when one of them nearly drowns, the school threatens to expel the ones who broke-in.

Gossip Girl takes pleasure in reporting that Serena has been spotted buying a pregnancy test, and word spreads like wildfire.

Charlie is finally starting to feel less like a fish-out-of-water with Serena and her friends, but complications present themselves when Charlie is invited to attend the Constance Billard alumni fundraiser. On the road to "happily ever after," Blair finds herself torn between the men in her life. Jack Bass' return to the Upper East Side sets off a chain of events that could end up destroying Chuck and those closest to him.

Season four wraps up with an explosive finale, including the return of Georgina Sparks and Constance Billard mean girls Kati and Is, a cameo by "Gossip Girl" author Cecily von Ziegesar, a performance by Airborne Toxic Event and, oh yeah, a few very juicy cliffhangers.

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 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.

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.

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.

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?

Serena hosts a big gala, Blair prepares to debut her new fashion line and Dan must decide if he is willing to sacrifice hisintegrity in order to get his work published.

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