When Gilded Age millionaires wanted to buy Italian Renaissance paintings, the expert whose opinion they sought was Bernard Berenson, with his vast erudition, incredible eye, and uncanny skill at attributing paintings. They visited Berenson at his beautiful Villa I Tatti, in the hills outside Florence, and walked with him through the immense private library--which he would eventually bequeath to Harvard--without ever suspecting that he had grown up in a poor Lithuanian Jewish...