As the summer draws to a close in the Hamptons, Serena and Nate have everyone fooled into thinking they are a couple to cover up the fact that Nate has been hooking up with a married, older woman. Blair returns from abroad with a hot guy on her arm, making a very jealous Chuck question his decision to leave Blair stranded at the heliport. Dan has spent the summer assisting a famous author. While interning for Eleanor Waldorf's company, Jenny sneaks an invite to a much-coveted Hamptons' White Party at which Eric introduces her to socialite Tinsley Mortimer.

Blair is ecstatic to land an internship at W Magazine, but the thrill quickly fades when she finds out that Dan has secured one of the coveted positions as well. Chuck may have finally met his match with Russell Thorpe – and his daughter Raina – back on the Upper East Side. Nate receives alarming news about his father’s business prospects.

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.