<P> `` Invasion '' is the fifth episode of the 6th season of the American television medical drama Grey 's Anatomy , and the show 's 107th episode overall . It was written by Mark Wilding and directed by Tony Phelan . The episode was originally broadcast on the American Broadcasting Company ( ABC ) in the United States on October 15 , 2009 . In the episode , the physicians of Seattle Grace Hospital must learn to co-operate with new Mercy West residents , who do not act in a kind manner to them . Other storylines include Dr. Callie Torres ( Sara Ramirez ) 's father returning to the hospital to condemn her homosexuality , and Dr. Izzie Stevens ( Katherine Heigl ) putting her career into jeopardy after administering the wrong treatment to a patient . </P>
<P> `` Invasion '' is the fifth episode of the 6th season of the American television medical drama Grey 's Anatomy , and the show 's 107th episode overall . It was written by Mark Wilding and directed by Tony Phelan . The episode was originally broadcast on the American Broadcasting Company ( ABC ) in the United States on October 15 , 2009 . In the episode , the physicians of Seattle Grace Hospital must learn to co-operate with new Mercy West residents , who do not act in a kind manner to them . Other storylines include Dr. Callie Torres ( Sara Ramirez ) 's father returning to the hospital to condemn her homosexuality , and Dr. Izzie Stevens ( Katherine Heigl ) putting her career into jeopardy after administering the wrong treatment to a patient . </P>
when do seattle grace and mercy west merge
when do seattle grace and mercy west merge
fifth episode of the 6th season
fifth episode of the 6th season