Kaylee Defer

When Ted and Barney argue about who has "dibs" on a hot girl, Ted realizes that she is there with Cindy (guest star Rachel Bilson), a girl he previously dated who is also the roommate of his future wife. Meanwhile, Robin is heartbroken over Don, and Marshall can't keep quiet about his desire to start a family.

When Robin learns that Barney never asked her father’s permission before proposing, she insists that he seek his approval before announcing their engagement. Meanwhile, Ted keeps his feelings concealed by throwing himself into planning their wedding.

Serena enlists Charlie to go undercover Gossip Girl-style to determine why Dan and Blair are spending so much time together, and what role an unexpected visitor is playing in their lives. With Nate’s help, Raina decides to go on a search for her long-lost mother. Chuck’s hopes about his legacy are dashed with the reveal of devastating information from the past.

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.

As Lily awaits the consequences of her decision, William van der Woodsen, CeCe and Lily’s sister, Carol, come into town to support her and be part of a Taschen photo shoot on "modern royalty" in which the Rhodes family is participating. Unbeknownst to Carol, who has always chosen to keep her daughter Charlie far away from the Upper East Side, Charlie has followed her to New York to meet Serena and the rest of the family. Blair has an epiphany about her future, and grapples with the knowledge of whom she’s destined to be with.