4. Brother's Keeper

Several patients are discovered to have the same rare infection, prompting Dr. Charles' daughter Robyn, an epidemiologist, to be brought in to find the common link. Dr. Choi and Dr. Rhodes work on an elderly man who is discovered to be very ill, but a conflict in how to best treat him develops between his son and his young girlfriend. Meanwhile, Dr. Reese tries to help a young drug addict and Maggie tends to a patient who is dear to her heart.