Official ABC synopsis
Entering their first year as residents after passing their intern exams, Meredith Grey, Cristina Yang, Izzie Stevens and Alex Karev now have interns of their own to mentor. Among the new crop of interns are George (forced to repeat his internship after failing his exams) and Lexie Grey, Meredith’s half-sister.

Meredith & McDreamy
Meredith met him in a bar the night before her first day of work, slept with him, then realized the next day that he was not just her boss, he was her boss's boss. She wanted nothing to do with him, but McDreamy chased her like a dog on a bumper, and she finally broke down.

Season 4
4-1 "A Change is Gonna Come" (09.27.07)
4-2 "Love/Addiction" (10.04.07)
4-3 "Let The Truth Sting" (10.11.07)
4-4 "The Heart of the Matter" (10.18.07)
4-5 "Haunt You Every Day" (10.25.07)
4-6 "Kung Fu Fighting" (11.01.07)
4-7 "Physical Attraction... Chemical Reaction" (11.08.07)
4-8 "Forever Young" (11.15.07)
4-9 "Crash Into Me, Part 1" (11.22.07)
4-10 "Crash Into Me, Part 2" (12.06.07)
4-11 "Lay Your Hands on Me" (01.10.08)
4-12 "Where The Wild Things Are" (04.24.08)
4-13 "Piece of My Heart" (05.01.08)
4-14 "The Becoming" (05.08.08)
4-15 "Losing My Mind" (05.15.08)
4-16 "Freedom, Part 1" (05.22.08)
4-17 "Freedom, Part 2" (05.22.08)

Meredith Grey (Ellen Pompeo)
Derek Shepherd (Patrick Dempsey)
Cristina Yang (Sandra Oh)
Izzie Stevens (Katherine Heigl)
Alex Karev (Justin Chambers)
George O'Malley (T.R. Knight)
Miranda Bailey (Chandra Wilson)
Richard Webber (James Pickens Jr.)
Callie Torres (Sara Ramirez)
Mark Sloan (Eric Dane)
Lexie Grey (Chyler Leigh)
Erica Hahn (Brooke Smith)