Grey's Anatomy Season 5 (Episode 8)

Title: "These Ties That Bind"
"One of Meredith's oldest friends, Sadie, becomes an intern at Seattle Grace, but Mer's friend is less than welcoming to her. Lexie leads her fellow interns in secretive, unorthodox surgical training sessions; and a new surgeon, Virgina Dixon, brings rules and order to the OR." (from wikipedia.org)