In the season premiere, Col. Ethan Willis (new cast member Rob Lowe) joins the team as part of a program in which the Department of Defense sends doctors to hospitals to teach new techniques and technologies that they learned on the field of combat. Willis and Mike take a harrowing chopper to Malibu to help save shark bite victims; Campbell (new series regular Boris Kodjoe) has become the head of both the OR and the ER in order to save costs, causing strife between him and Leanne; and Jesse welcomes a new round of residents. Noah Gray-Cabey, Emily Tyra and Nafessa Williams join the cast in recurring roles as new residents in the ER.