Grey’s Anatomy Season 6 Episode 4 “Tainted Obligation”. Meredith is facing the, maybe, most difficult situation in her life when she was assigned to perform a surgery for her father (Thatcher) who was brought back to the hospital because of a failing liver. Lexie does everything to help her while giving the comfort and care their father needed. Meanwhile, Mark gets annoyed with Cristina’s competitive zeal and tries to trick her into assisting an unusual surgery. On the otherhand, Izzie empathizes with a patient puzzled with tumors. Watch this episode as more drama unfolds in the Season 6 of Grey’s Anatomy. Watch Grey’s Anatomy 6 Episode 4 s06e04 “Tainted Obligation”! It will be aired on Thursday, October 8 at 9:00 PM over ABC.