The team takes on the case of 6-year-old Lucy, who collapsed at daycare. They discover that the tissues surrounding Lucy's heart have hardened and are strangling her heart, a condition usually found in much older patients. As the team searches for an explanation, Lucy's condition worsens and she suffers a stroke. There's a palpable tension between Cameron and Chase, and House intentionally assigns them tasks to do together, including a trip to Lucy's house to check for any possible environmental explanations for her condition. While there, they discover surprising evidence indicating that Lucy may have been abused. Lucy's 8-year-old brother develops a not-so-innocent crush on Cameron, and as he becomes increasingly aggressive, House suspects that whatever is killing Lucy has begun to affect her brother, too. As they try to narrow down what is causing Lucy's condition before it's too late, House and Cameron clash over how to treat her. Meanwhile, when Wilson takes Cuddy out to see a play, House puts ideas in Wilson's head regarding Cuddy's motivation for going with him.