While Morgan thinks it's nothing serious when San Francisco Symphony violinist, Jas Kohli, arrives at the ER with an infection in her left index finger, Shaun suggests checking her for flesh-eating bacteria, even though the test could not only damage the finger but threaten her career. Although Morgan continues to downplay the likelihood of bacteria, a biopsy reveals that Shaun is right and Melendez orders surgery to save her hand. When 13-year-old Riley Mulloy is brought to the ER with an uncontrollable nose-bleed, her parents suspect a stress reaction to their divorce several years ago. But as Bruce and Stella are arguing, Claire worries it could be more complicated when Riley complains of breathing problems and starts coughing up blood. Meanwhile, as Shaun and Lea struggle to find their way as roommates, Glassman resists having a hospital-assigned caregiver. As she gains Riley's confidence by noting the similarities in their teenage experiences, Claire recommends a CT scan. Though Park warns that it could needlessly expose her to radiation, Claire persuades Lim that its worth the risk. When Riley suddenly worsens, her parents authorize an exploratory surgery that suggests a tumour. But once the doctors find that the unidentified mass is really a toy building block she swallowed as a young child, they remove it and solve the problem, bringing Riley and her new friend, Claire, even closer. Meanwhile, as Shaun and Lea look for advice on resolving their troubles, Glassman's mood improves when his friend, Debbie, drops by to see him.