Season 6, Episode 15: "The Time Warp"
"The Time Warp" has nothing to do with The Rocky Horror Picture Show, but it's still a blast. Derek suggests that Richard give a last lecture if he plans to leave the hospital. So the surgeons, including the former chief, recall their most pivotal cases. Young Richard and Ellis (played by THE Sarah Paulson) fall in love and take on an AIDS patient. Plus, we see Callie having a throwback moment with Alex and a shy past Dr. Bailey standing up to her snotty supervisor. Other than the fact that we're seeing Ellis's marriage crumbling, it's a satisfying episode where good prevails.