Based on a true story, in 1916, mining engineer Oliver Woodward (Brendan Cowell) has to leave his new young love behind to join the 1st Australian Tunnelling Company in the mud and carnage of the Western Front in World War I. Deep beneath the German lines, Woodward and his secret platoon of Australian tunnelers struggle to maintain and extend a leaking labyrinthine tunnel system packed with enough high explosives to change the course of the war.