Alex's newest patients are a pair of adult conjoined twins who have learned how to not only survive but also thrive together. Unfortunately, one sister, Beth, has cancer, and because the other sister, Emily, has a heart condition, it isn't safe to treat the cancer unless the sisters are separated. The sisters refuse a separation surgery, stating that they would rather die together than live without each other.
Their deep connection causes Alex to question what it means to be truly connected to another person. She remembers her heartbreak as an intern when Jesse, with whom she was having an affair, left for another job. She also remembers her first meeting with Pierce, who already seemed to know they shared a mutual destiny. In the present, Alex continues to struggle with Pierce's desire for a bigger commitment, but she lets him know that, while change is hard for her, she's working on it.
Meanwhile, Dr. Callahan realizes he has MRSA and will have to contact everyone he's had intimate relations with in the past six months. Ji-Sung is shocked by the number of attractive women who show up to be screened for the infection and to learn how much they all like Callahan. Ji-Sung can't help but wonder if there's more to Callahan than she realizes.
When Beth's health further deteriorates, she agrees to the separation surgery. Although Emily is resistant at first, after she sees how much pain her sister is in, she also consents. The surgery takes over 24 hours, and Alex is there for all of it. She's also there when the sisters wake up, able to look each other in the eyes for the first time.
