History geeks, this is your Fringe show. In this no-frills staging, the American Civic Forum focuses on a slice of U.S. history to reveal larger truths. Linda Sue Anderson gives a powerful, nuanced portrayal of pioneering nurse Clara Barton, the “Angel of the Battlefield,” as she testifies to Congress after the Civil War. Much of the script comes straight from that testimony, the first given to Congress by a woman. She tells us about the horrifying conditions at Andersonville prison in Georgia, where she traveled to document missing and dead Union soldiers. She recounts conversations with “neighborly” white southerners quick to blame the atrocities on two prison officials who had recently, and conveniently, died. “Themselves,” she notes, “they made immaculate.” One tip: Read the program notes before the show begins. (10 p.m. Sun., 10 p.m. Fri. Aug. 11, 4 p.m. Sun. Aug. 13, Bryant-Lake Bowl, 810 W. Lake St., Mpls.)