An exclusive group of privileged teens from a posh prep school on Manhattan's Upper East Side whose lives revolve around the blog of the all-knowing albeit ultra-secretive Gossip Girl.
After a brief encounter abroad, Chuck and Blair make a promise to each other about their relationship, which leaves them once again apart. Dan, with some help from an unlikely ally, Georgina, is writing a scathing tell-all book that can only mean trouble. As the sole head of The Spectator, Nate is making his own decisions and is ready to go up against Gossip Girl. As word spreads that Serena is missing, the gang bands together to find her and are shocked by what they find.
Trying to prove herself in adult society, Serena hosts the Central Park Conservancy’s big gala, of which she is now the newest Board Member, and she and Nate both learn something shocking about their significant others. Blair prepares to debut her new fashion line, but a rival from her past holds the key to her future. With the help of Georgina, Dan lands some meetings with publishers, but he must decide if he is willing to sacrifice his integrity in order to get his work published. Meanwhile, Chuck tries to persuade Amira to help him look into his father’s past, even if it means jeopardizing Lily and Bart’s relationship.
Feeling the pressure to make her first Waldorf Designs fashion show a success, Blair must rely on help from an unlikely source, but some unexpected scheming causes a scandal on the runway. Serena discovers that befriending Steven’s daughter Sage is trickier than she thought, especially when she is forced to put her issues with Blair aside to make Sage happy. Nate publishes Dan’s first serialized article causing a stir and producing a serious threat. Meanwhile, Chuck begins to look into the clue that Amira left behind, which may help uncover what Bart is hiding.
Chuck’s continued investigation into his father’s dealings leads him to an unlikely event with Manhattan’s elite, where he hopes to find the one person who can tell him the truth about Bart. Serena and Steven decide to reveal their romantic histories so they aren’t surprised by anything, but neither was prepared for what they uncovered. With The Spectator in jeopardy after Dan decided to publish elsewhere, Nate must make a difficult decision to keep it in business. Meanwhile, Georgina pushes Dan to choose a worthy person to date to boost his image, but he finds himself drawn in a different direction.
After Eleanor gives Blair an ultimatum, Blair is even more determined to remedy Waldorf Designs’ problems by making a splash with a dress at the upcoming Cotillion, but a shocking revelation at the ball affects everyone. Serena becomes worried about Steven’s attitude toward her, but after some investigating she discovers the surprising reason why. Chuck finds an unlikely ally as he tries to drive a wedge between Bart and Lily’s relationship to help expose his father’s secret. Meanwhile, Dan publishes another article, but the effect is just the opposite of what he was hoping for.
Serena volunteers to help Dan find a new place to live but their time together brings up unexpected emotions.
Serena and Dan realize that they need to make amends with the people they have wronged. Chuck’s search for evidence of his father’s illegal activities leads him to a showdown with Bart.
Serena and Dan decide to throw their first Thanksgiving together, inviting only their closest friends, but everyone seems to have their own agenda for attending. Feeling defeated by his father, Chuck begins a downward spiral, leaving Blair to find a solution to his problems. Meanwhile, Dan has written his latest exposé, but he must make a tough decision whether to publish it, knowing it could destroy a close friendship.
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.
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.