Season 6 Episode 4

Title: Tainted Obligation
Air Date: October 8, 2009 at 12:00 AM PDT

When Meredith and Lexie's father, Thatcher, returns to the hospital with a failed liver, it's up to Meredith to save his life. Meanwhile, Izzie empathizes with a patient riddled with tumors, and Mark, annoyed with Cristina's competitive zeal, tricks her into assisting on an unusual surgery.