For most people the image of the collapse of the World Trade Center Towers on Sept. 11, 2001, was not only a scene of unforgettable horror, it was a moment of unimaginable consequence. This follows a blue ribbon team of forensic engineers as they begin searching for clues that would tell them why the towers fell. From detailed examination of the buildings original design to the relentless process of searching the scrap steel yards and Ground Zero itself for evidence.