Susane E. Lee

Derek decides to quit after learning that more of his patients have died than survived; Izzie's interns make an unsettling discovery about "Patient X."

Harbor School's senior prom brings out the best and the worst in everyone. Taylor (recurring guest star AUTUMN REESER) has a great time, while Summer doesn't enjoy herself with her surprising prom date. Seth and Anna (recurring guest star SAMAIRE ARMSTRONG) come up with a plan to win Summer back for Seth. Meanwhile, Marissa convinces Volchok (recurring guest star CAM GIGANDET) to go to the prom with her, and Ryan brings an unexpected old flame. When one of the girls is elected prom queen, it truly becomes a night to remember. Later, when Taylor's prom funds are discovered to be missing, Ryan returns to his old ways, and prom night turns brutal. LISA TUCKER ("American Idol") guest stars as herself.

Rory is touched when Emily and Richard throw a party to introduce her to their Yale alumni friends; when Dean arrives at the party to pick up Rory, it is clear to him that he has no place in her privileged world.

After Richard and Emily renew their vows, Lorelai, Luke and Christopher find Rory and Logan together.

When a fabricated video makes it look like Elizabeth and Henry are making fun of a foreign dignitary, they struggle to convince him not to pull out of an important international agreement. Also, Stevie says goodbye to an important person in her life.

Rory is disappointed when Logan doesn't invite her to be his date at a book-signing party thrown by his father; Richard spies Emily talking to a former flame and rear-ends her car, forcing an opportunity for reconciliation.