“The Underground Girls of Kabul: In Search of a Hidden Resistance in Afghanistan,” delves into the practice of “bacha posh,” in which prepubescent Afghan girls are dressed and passed off as boys in families, schools and communities. Through extensive interviews with former bacha posh, observation of present ones and conversations with doctors and teachers, Nordberg unearths details of a dynamic that one suspects will be news to the armies of aid workers and gender experts in post-invasion Afghanistan.