Le Gheer, Belgium - July 5th 1955 - 26,000 lbs of high explosives - a MINE - laid deep beneath the German trench lines during the First World War, detonates in a thunderstorm. It leaves a crater 250ft in diameter and 60ft deep! It is one of several charges known to be lying dormant under the battlefields of the old Western Front and one of potentially hundreds of mines abandoned at the end of the war by the men who had laid them. Narrated by actor John Shrapnel, "One of Our Mines is Missing! skilfully weaves past and present as it unfolds the story of the search for one of these mines - The Broadmarsh - deep within the bowels of the Canadian Memorial Site at VIMY Ridge, France. Rare archive film and photographs, unique privately sourced images, sophisticated 3D animation and superb aerial photography bring the troglodyte world of the tunnellers to life. And, for the first time ever, cameras take us into the heart of not one, but TWO mine chambers as British Army explosives experts attempt to defuse the potentially lethal packages within.