GREY'S ANATOMY - "P.Y.T. (Pretty Young Thing)" - Thatcher Grey, Meredith and Lexie's father, returns to Seattle Grace with stomach pains and a new, twenty-something tattooed girlfriend, Danielle. Meanwhile, Alex clashes with the new OB, Dr. Lucy Fields, over a patient and Mark places Jackson on his service in exchange for information on Lexie, on "Grey's Anatomy," THURSDAY, FEBRUARY 10 (9:00-10:01 p.m., ET) on the ABC Television Network. (ABC/ERIC MCCANDLESS) JEFF PERRY, ALEXA HAVINS