15. IZZIE'S DAUGHTER
Season 3, ''Time After Time''
What a small world it is when the child Izzie (Katherine Heigl) gave up as a teen reemerges at Seattle Grace in need of a bone marrow transplant. Of course the do-gooder suffers through the painful donor test, even though the adoptive parents won't let Izzie visit her doppelgänger.
Inseparable lovers, conjoined twins, a dead Meredith -- as we return to Seattle Grace tonight, we rank the most riveting patients and plot lines to pass through its halls