Television viewers all over the world are familiar with the iconic images of destruction and devastation that followed the collapse of the Twin Towers. What people don't realise is that underneath the gargantuan mountain of rubble that greeted rescuers was an extraordinary world, hundreds of feet deep, which held even more incredible stories. 9/11: Ground Zero Underworld presents the personal stories of those who searched tirelessly for their loved ones, sifting through tonnes of debris in an attempt to bring them home to rest. In the hours and days following the disaster, relatives and friends of those inside the buildings descended on Ground Zero, vowing to find their loved ones, dead or alive. And so began one of the greatest search operations in history - a story of extraordinary courage, perseverance and humanity.