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.

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.