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Invasion (Grey's Anatomy) "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.
Mercy (Duffy song) "Mercy" is a song performed by Welsh singer Duffy, released as the second single from her debut studio album, Rockferry (2008). Co-written by Duffy and Steve Booker and produced by Booker, it was released worldwide in 2008 to critical acclaim and unprecedented chart success. As Duffy's first international release, the song is credited with firmly establishing her career and is now considered her signature song. "Mercy" received comparisons to Duffy's previous single, "Rockferry". Critical reviewers of "Mercy" noted similarities between the song to releases by Aretha Franklin, Dusty Springfield and The Supremes, as well as contemporaries such as fellow British singer Amy Winehouse.