Start by placing them across the board from each other: two queen’s bishops, rows of squares ahead of them. One is Noel Scott Engel, born in Ohio in 1943, an American who went to Britain for fame and who stayed there; the other is David Robert Jones, born in Brixton on the day before Engel’s fourth birthday, who scrabbled for fame in Britain and, once he finally got it, left for good. Jones became David Bowie, Engel became Scott Walker. Each was precocious, ambitious, beautiful. They first met around 1966 at a London nightclub, The Scotch of St. James, when Walker was a pop star and Bowie nothing but polite aspiration.