There’s no shortage of plays that read like classroom exercises–but Chicago playwright Belinda Bremner conceived Envoy precisely for the purpose of training actors. The story revolves around student volunteers on a philanthropic service project in an unnamed third-world country who are taken hostage by rebel guerrillas. The actors playing the diverse characters in this Echo Theatre Company debut production are given several interpretive options, and at each show a different performer makes an unscripted choice that determines the ending. But the many earlier dramas in this genre can’t help but make the characters’ responses and the artificial crises here predictable. This play’s more useful for promoting discussion than illuminating facts. –Mary Shen Barnidge a Through 9/16: Thu-Sat 7 PM, Sun 2 PM, Theatre Building Chicago, 1225 W. Belmont, 773-327-5252, $15.