Eleven ironworkers eat their lunch sitting on an iron beam. They don't seem to care that their feet are dangling in the air high above New York, with Central Park and a foggy Manhattan in the depths below them. Everybody knows the photograph "Lunch atop a Skyscraper," taken during construction of the RCA Building at Rockefeller Center in 1932. The image became an icon of the Great Depression. But its backgrounds remain mysterious: despite extensive research, neither the 11 men nor the photographer have been definitively identified. When director Seán Ó Cualáin stumbled upon a copy of the picture in a pub in a small Irish hamlet, with a note that two of the men came from that village, he decided to delve into the history of the photo. The resulting film gives new depths to the iconic image - even in a literal sense, through digital manipulations of the original. Narrated by actress Fionnula Flanagan, we travel to the Rockefeller archives (which store many more images of derring-do during construction) and the Corbis archive, which houses the original glass plate photo. We also visit experts such as documentary filmmaker Ric Burns and photographer Joe Woolhead, who follows in the footsteps of his anonymous predecessors as he documents the current rebuilding of the World Trade Center.