Jessica Lucas — Billie Sutton — Jessica Lucas — Billie Sutton

Lucas entered in season 4 as neurosurgeon Billie Sutton and became central through the final two seasons. Earlier audiences knew her from Cloverfield, Evil Dead, Gotham, and Cult.

After The Resident, she joined CSI: Vegas. Her late-series arrival illustrates how an established ensemble can introduce a character with independent history rather than merely filling a departed role.