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Invasion is the fifth episode of the sixth season of Grey's Anatomy, and episode one hundred and seven overall.
Starring: Ellen Pompeo (Meredith), Sandra Oh (Cristina), Katherine Heigl (Izzie), Justin Chambers (Alex), Chandra Wilson (Miranda), James Pickens, Jr. (Richard), Sara Ramirez (Callie), Eric Dane (Mark), Chyler Leigh (Lexie), Kevin McKidd (Owen), Jessica Capshaw (Arizona), Patrick Dempsey (Derek)
Guest Starring: (in credits order) Robert Baker (Dr. Charles Percy), David Bowe (Don), Sarah Drew (Dr. April Kepner), Alexie Gilmore (Sarah Freemont), Jack Gwaltney (Frank Noosebaum), J.P. Pitoc (Billy), Brandon Scott (Dr. Ryan Spalding), Kathleen Wilhoite (Leslie Goldman), Jesse Williams (Dr. Jackson Avery), Nora Zehetner (Dr. Reed Adamson), Bruce French (Father Kevin), Freda Foh Shen (Missy Grant), Hector Elizondo (Mr. Torres)