You can see her dark-eyed beauty in photos by Walker Evans, and her bewitching figure in paintings by Lucian Freud. She is the mermaid of whom poet Robert Lowell writes in The Dolphin (and he was clutching her portrait when he died). She was Lady Caroline Blackwood, legendarily witty and alluring but also a legendary drunk. Raised an heiress to the Guinness fortune, Blackwood (1931-1996) moved easily among the aristocracy, the bohemians of postwar England and the liberal intelligentsia of 1960s New York. She has been called a muse to genius -- though her marriages to Lucian Freud, the composer Israel Citkowitz, and Robert Lowell were as troubled as they were inspiring -- and she was an author herself, short-listed for the Booker Prize in 1977. In this first biography of Blackwood, Nancy Schoenberger deftly paints a complex woman who was captivating to her dying day.