A fist fight breaks out between Derek and Karen's beau Dev, while the fear of losing everything causes a friction between Julia and Eileen.
A movie star may steal the limelight from Karen and Ivy when "Smash" returns next week. Uma Thurman will guest star in the upcoming episode as the mercurial Rebecca Duvall, who can boost "Marilyn". However, Eileen gets a new problem when Rebecca gets stuck in Cuba.
Derek puts Karen in as understudy, but she must learn to perform under extreme pressure as he threatens to break her will. Meanwhile, her relationship with Dev is put to the test as the latter asks if the former is willing to give up her acting career.
Tension also rises between Julia and Eileen, who claim they're are at risk of losing everything, as well as between Derek and Dev, who will be involved in a fist fight. Meanwhile, Tom and Julia celebrate their anniversary with a ritual, and face some hard truths about what show business can do to relationships.
"Understudy" will air Monday, April 9 at 10/9c on NBC.