During World War One, a barbaric war was fought deep beneath the trenches, in a maze of tunnels and dugouts over 10 metres underground. This secret front was home to thousands of soldiers, who fought the enemy using knives, fists and explosives. The Underground War traces an unprecedented hi-tech search for one of the last Allied dugouts, deep beneath the cornfields in Flanders, Belgium. An international team of archaeologists and historians must find its entrance, pump out thousands of litres of water and then attempt to excavate this relic of the Great War. Their challenge is to discover how big it is, and what role the Vampire dugout played in the aftermath of the Battle of Passchendaele.