During Argentina's Dirty War (1976-83), thousands of adult children disappeared after being abducted by that country's military dictatorship. Their mothers didn't let this go unnoticed. Known as the Mothers of the Plaza de Mayo, they began marching every week in Buenos Aires, beginning in 1977, to demand answers. Their courage and dedication are memorialized in dance by the Wylliams/Henry Contemporary Dance Company, during its 20th anniversary concert. For 20 years, the KC-based company has drawn from a wide variety of sources to inspire thought-provoking, energetic modern dance, moving through abstract art, social issues, pilgrimages and existential crises. Also part of the 8 p.m. performance at White Recital Hall in the UMKC Performing Arts Center (4949 Cherry): the company premiere of "Session for Six" by Anna Sokolow. Tickets cost $18 or $24 for adults and $15 for students and seniors; see wylliams-henry.org or call 816-235-6222.