When Trethewey was 19, her abusive stepfather killed her mother. In the 35 years since, she says, “I wanted to forge a new life for myself that didn’t include that past, but, of course, that was impossible.” In her new memoir, ‘Memorial Drive,’ Trethewey revives her mother’s memory and shares stories about growing up biracial in the South. She was the U.S. Poet Laureate in 2012 and 2013.