Stella provides the team and Gregory House with insight into her mother's case. The team first gets suspicious when Margo goes through tremendous mood swings when Stella comes to visit and Margo tells her husband (Stella's stepfather Ted Dalton) that she asked him not to bring her to the hospital.
Later, Stella goes exploring and House finds her. As they walk back to Margo's room, House starts questioning Stella and learns that although her parents never fight, and they talk about having another child all the time and why the fertility medication she's been taking isn't working. House soon realizes that Margo's personality won't let her confront her husband about her wish to stop having children as her life with Stella and her career already keep her very busy - so busy she has been taking ritalin to cope. He confronts Margo with this information and accuses her of taking the pill along with her fertility medication - a combination that would perfectly explain her symptoms.
Stella also shows a great deal of insight into House's personality, asking if his hurt leg is why he's so sad all the time. House deflects the question and says he's just "...complicated. Chicks dig that."