Need a refresher course on what the good docs at Seattle Grace Hospital are up to? ET has the A to Z on Izzy (KATHERINE HEIGL), Derek (PATRICK DEMPSEY), Meredith (ELLEN POMPEO), George (TR KNIGHT), Alex (JUSTIN CHAMBERS) and Mark (ERIC DANE) before the series returns with new episodes on Thursday, April 24 at 9 p.m. on ABC.