NOVA returns to Ground Zero to witness the final chapter in an epic story of engineering, innovation, and the perseverance of the human spirit: the completion of One World Trade Center, the skyscraper rising up 104 stories and 1,776 feet from the site where the Twin Towers once stood. In this update of NOVA's "Engineering Ground Zero, " which featured behind-the-scenes access to the struggles of the engineers and architects working at 1 WTC and the National September 11 Memorial and Museum, NOVA goes inside the construction of the new tower's final floors and the installation of its soaring, 800-ton spire and beacon. But 1 WTC isn't the only engineering marvel taking shape here: NOVA goes underground to see the construction of a multi-billion dollar transit center whose sweeping, sinuous design is said to be inspired by the shape of a bird being released from a child's hand. Will the buildings be completed on time under competing business, environmental, and safety demands? And will the final product be a fitting site for national remembrance?