Derek's sister Nancy (Embeth Davidtz) pays a visit for the express purpose of giving him Hell about the "slutty" Meredith (Ellen Pompeo), all the while blissfully ignorant of Addison's infidelity. Cristina (Sandra Oh) inspires envy when she helps perform a rare cardiac autotransplantation (aka the Humpty Dumpty procedure), but her actions just before surgery serve only to arouse suspicions about Burke (Isaiah Washington). Addison (Kate Walsh) and George's (T.R. Knight) pregnant patient Noelle (Liza Lapira) is in a strange predicament: she has two uteruses, and one of her babies is growing faster than the other, indicating that she's been unfaithful to at least one of the fathers. And finally, Alex (Katherine Heigl) toys with the idea of retiring as a doctor and using her multi-million-dollar inheritance to start another business. ~ Hal Erickson, Rovi