In Thrall (Houghton Mifflin Harcourt, $23), her fourth collection, the U.S. Poet Laureate Natasha Trethewey wrestles with her family’s history and her own biracial identity. “Elegy,” a poem dedicated to her (still living) father, caustically poses the rhetorical question: “What does it matter / if I tell you I learned to be?” “Help, 1968,” focuses on a Robert Frank photograph of a white child and its black nanny, which Tretheway uses to share a family story of how her own mother, an African-American woman, was frequently mistaken by strangers for Trethewey’s maid. “I think of the betrayals of flesh,” she writes. “Carrying me / each day—white in her arms—as if / she were a prop: a black backdrop, / the dark foil in this American story.” Through sharp descriptions of 17th- and 18th-century paintings, Trethewey traces the lexicography of bodies once labeled mulatto, quadroon, and mestizo, and examines the damaging social and psychological legacies of this racism. With her sweeping and intimate poetry, Trethewey beautifully illuminates how “so much is left / untold… / between what is said and not… / the way the past unwritten / eludes us.”