"What is there I will not let go?" asks the introductory poem in Ghost Guest. With effortless authority, Rachel Hadas's new collection keeps answering that question. Memories of places and people segue to elegies, which lead to meditations on art and poetry, mythology and, especially, teaching. Dreamy yet precise, celebratory yet attuned to mortality, these valedictory poems tell us exactly what crucial and intangible things Rachel Hadas will not let go.