S2, E4: Several patients are discovered to have the same rare infection, prompting Dr. Charles' (Oliver Platt) daughter Robyn (guest star Mekia Cox), an epidemiologist, to be brought in to find the common link. Dr. Choi (Brian Tee) and Dr. Rhodes (Colin Donnell) 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 (Rachel DiPillo) tries to help a young drug addict and Maggie (Marlyne Barrett) tends to a patient who is dear to her heart. S. Epatha Merkerson, Yaya DaCosta, Nick Gehlfuss and Torrey DeVitto also star. Jeff Hephner, Patti Murin and Ato Essandoh also guest star.