Blair’s dreams appear to be coming true, but Serena threatens to jeopardize it all by dredging up Blair’s past. Charlie befriends Vanessa, who may or may not have a hidden agenda. Nate is torn between his relationship with Raina and a truth he must keep hidden out of loyalty to Chuck.

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.

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.

Serena loves her new job in Hollywood, but makes a costly misstep when she tries to impress her boss. Chuck and Nate arrive in Los Angeles as the last stop of their Lost Summer trip, joining Serena at a glamorous Hollywood Hills party, where Nate meets a sexy older woman. Blair and Louis return from Monaco and begin planning their royal wedding, but when Louis refuses to stand up to his family and support Blair’s choices, his weakness threatens their relationship. A magazine is planning to run an excerpt of Dan’s book until an unlikely ally steps in to help him kill the story.

In the midst of celebrating Yom Kippur with family and friends, Blair and Louis find themselves in a power struggle with Louis' family. Serena's boss puts Serena in the awkward position of choosing between her new job and her relationship with Dan. Diana prepares to debut the New York Spectator, but an unfortunate last-minute surprise delays the launch and Diana expects Nate to do whatever it takes to save the day.

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.

Blair must make a difficult decision about her future, the consequences of which could hurt those she loves most. Serena takes the blame for an incident with Gossip Girl in order to protect someone she loves.. Georgina smells the scent of scandal and decides to follow its trail.