For a bracing reminder of the awful consequences of ingrained bigotry, Park Square Theatre is presenting playwright Hansol Jung’s stirring Cardboard Piano. The Uganda-set drama is structured in two acts, the first of which concerns the love of two female teens, one a local Ugandan, the other the daughter of American missionaries. Compelled to hide their culturally denounced relationship, the girls hold a secret ceremony to exchange matrimonial vows—only to have their private moment broken by the arrival of a child soldier who serves as a prelude to imminent violence. Leaping ahead 15 years, the second act examines the haunting consequences of that fateful night, drawing a connective line between tragic past deeds and the possibility of forgiveness and redemption. Featuring a quartet of actors (Ansa Akyea, Kiara Jackson, Michael Jemison, and Adelin Phelps) under the direction of Signe V. Harriday, Cardboard Piano suggests that, given enough time, even the most appallingly brutal proponents of hate have the potential for change.