In sinuous, murky first fiction from ex-Harvard lit prof Richards (Imperial Archive, etc., not reviewed), the memory of Vietnam continues to plague the lives of four people who were involved in the failure, in 1973, of a massive dam built to control the mighty Mekong River. Thinking his brother, an outsider, can unravel the tangled threads of their stories, Harper, one of the four, persuades the emphatic Gailly to listen. Complex memories of other rivers and dams color each person's Vietnam connection: Harper's memories have to do with an idyllic riverside life that ended when the Monongahela was dammed, flooding his Pennsylvania home. He eventually became the commander of an armada of gunboats, patrolling the Mekong on the day the dam went into service. Petard, an American Indian and the project's chief engineer, who saved Harper's life, first became obsessed with dams when his tribe was displaced by one on the Klamath River; revenge drives him to engineering school and a career with the Bureau of Reclamation, where he quietly works to sabotage projects. Travers, a brilliant Harvard entomologist whose ideas of insect behavior fueled the Bureau's decision to dam the Mekong, finds his opposition to the dam shaped by the ancestral memories of a female Puritan forebear whose heretical notions of altruism he has unwittingly embraced. And photographer Jenna, whose images of the dam showed deep cracks where none were otherwise visible, had her feelings shaped by contact with the French dam builder Defosse, who believed that ritual human sacrifice was required to preserve a dam. Not until Gailly gets the skinny from the Bureau's director, however, can he make sense of the mix of anger, obsession, and arrogance that contributed to the dam's catastrophic failure. Often reminiscent of an exercise in multidimensional puzzle- solving, Richards's fiction debut is as alluring as it is mind- bending. Too bad that in the end the revelations accumulated here, like the imaginary dam that brought them together, fail to hold water.