For three years along the Western Front, German and French engineers fought a war beneath the war, digging galleries under no-man's-land to pack them with explosives and blow the enemy's trenches into the air. The film reconstructs this tunnel campaign around a small French town that became its epicenter, using the preserved diaries of Herman Hoppe, a German engineer who helped build many of the mine shafts himself. His firsthand account carries the narration through the claustrophobic mechanics of the fighting: listening for the enemy digging toward you, racing to detonate first, and living for months in tunnels that could collapse or explode without warning. Historians and archival photographs fill out the wider picture of a front where the real battle often happened yards underground rather than above it. The result is a account of one of the war's stranger fronts, told less through grand strategy than through the diary of a man who spent years digging toward people trying to kill him first.