Photo provided by Mixed Blood Theatre To be an understudy or alternate in a show is like wearing clothes made for someone else's body. The contours of the performance — from gestures to blocking — have been made for you. "If you are a replacement performer, you have to replicate the performance of the person whose role you're taking over," said Jack Reuler, artistic director of Mixed Blood Theatre. "Your job is to capture the essence of something in a template not of your own making." By all accounts, that is what Sha Cage is doing in Lynn Nottage's "Ruined," the gut-wrenching play about women finding sanctuary in a brothel in a war zone in Congo. Cage took over the role of Josephine, the brothel owner's assistant, for the last three weeks of the run of the show, which closes this weekend at Mixed Blood. She replaced Erika Ratcliff, a Chicago-based dynamo who had pre-arranged to only do half the run of "Ruined"; she left in another production in Baltimore. It is true that "when you move into an understudy part, you have to model what's been done," said Cage. "But with this, I don't feel like I've been crippled by that. [Director] Aditi [Kapil] has given me license to make it my own." The mother of seven-month-old boy, Cage attended rehearsals for the show, learning alongside Ratcliff the blocking and nuances of the part. And she had put-in rehearsals with the cast that helped her get her legs quickly. Cast-member Aimee Bryant, who has one of the most evocative scenes in the drama, said that Cage has moved seamlessly into the production. "Any new person coming into a show changes the whole rhythm," she said. "Sometimes its for the better or worse. Sometimes it's just different. The trick is to do somebody's work in your own body. Sha is doing a great job." Comparisons are inevitable in a situation where an understudy or a replacement actor enters the picture. Cage and Ratcliff are of different heights. "Erika is a lot taller than Sha and is broader in her shoulders," said Bryant. "She was more intimidating than Sha, very forward and aggressive. Sha is more laid back but she has another type of intensity." Replacements are commonplace in theater. "Ruined" stars Regina Marie Williams as Mama Nadi in the same stage where she earlier this year played a slave woman in Carlyle Brown's "Pure Confidence." On Monday, the New York production of that drama won three Audelco Awards, including for director Marion McClinton and "Ruined" cast-member Gavin Lawrence. Williams was supposed to go travel with "Pure Confidence" when it transferred to an off-Broadway playhouse in the spring. But she was cast in "Caroline, or Change" at the Guthrie Theater. Another actor, Christiana Clark, took over the role.