We spend three momentous holidays—Thanksgiving, Christmas and New Year's Eve—with the staff of Seattle Grace.
Mark—and we—are stunned when a beautiful blonde walks into the ER and tells him, "I'm pretty sure you're my dad!" Turns out, she's right, the product of a youthful affair that Mark would rather forget. Mark feels so guilty, he lets 18-year-old Sloan (yes, her mother named her after him!) stay with him and Lexie indefinitely. Lexie is a champ—even if she cuts off part of her finger at the news that Sloan is moving in—but finally gives Mark an ultimatum: "No more sex until you talk to her." Sloan says she knows she's overstayed her welcome, but confesses she's pregnant and has nowhere else to go. Mark hugs her and lets her stay.