Tunnels and craters in the heart of a French coalfield hide horrors from the First World War. More than 50,000 British soldiers were killed or wounded here in a hellish battle that moved underground. Our team of archaeologists, historians, and forensic experts is here to excavate the lip of a gigantic crater that was created by a massive underground explosion. They discover a mass grave and, within the burial site, clues to one of the fallen soldiers, a German from Bavaria. A simple uniform button, a regiment number on an epaulette, and a postcard inside a music book, lead to the identity of this soldier: a gifted violinist named Leopold Rotharmel turned warrior in the German unit that would later be called the Storm Troopers.