ON August 7, 1974 a man stepped out on a thin high wire tied between Manhattan’s famous Twin Towers. Phillipe Petit, a skinny French tightrope walker, cast a rope between the two buildings of the World Trade Center with a bow and arrow in the night, and his illegal, crazy but ultimately successful walk between the two iconic buildings would eventually come to be called the art crime of the century. For Dublin-born writer Colum McCann, 44, Petit’s daring 1974 tightrope walk was a jumping off point, irony intended, a way to talk about New York, the Twin Towers and the people of the city and what they mean to him, without instantly conjuring up images of sirens and dust and devastation.