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.

Blair returns to school after losing Queen Bee status; Serena's not fond of living with her future stepbrother, Chuck.

Serena's world is turned upside down when her former partner in crime, Georgina Sparks, returns to Manhattan to stir up trouble.

Blair and Jenny escalate their "popularity war" by spreading scandalous rumors about each other through Gossip Girl.

When Dan starts getting cozy with Amanda, the new girl at school, Serena turns to Blair and her minions to step in to sabotage her chances. Vanessa also enlists Blair's help when she finds out a scandalous secret about Catherine.

Blair sabotages her mother's show at Fashion Week; Dan starts hanging out with Chuck, and learns that a walk on the dark side always has risks.

Blair seeks revenge by enticing Chuck to seduce Vanessa; Serena rebels at a party of Lily's; Dan and Jenny find out a secret Nate has been hiding.

Dan tries to get close to Bart Bass to possibly write an exposé, but things get heated when Chuck finds out.

The teens prepare for the annual Snowflake Ball, a charity event for prep school seniors.

Chuck's uncle, Jack Bass, arrives on the scene; Jenny returns to school and takes on the mean girls.

Bart's will is read and everyone learns the fate of the Bass empire; Dan discovers the secret between Rufus and Lily.

The seniors try to find out who is worthy of an early admission to Yale; Chuck pairs up with an unlikely ally in his war with Jack over Bass Industries.

Blair comes up with a plan to get revenge on her teacher; Chuck wakes up in a hotel and tries to piece together what happened the night before.

The seniors put on a production of "The Age of Innocence"; Chuck enlists help from an unlikely source -- his nemesis, Carter Baizen.

Serena throws Jenny a party for her 16th birthday, but things get out of control when Poppy Lifton turns the small gathering into a huge social event.

To prove her independence, Serena refuses to leave jail with her mother or her grandmother; Rufus is furious with Lily for having Serena arrested.

Gossip Girl livens things up at graduation by sending out a shocking email blast during the ceremony.

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.

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.