Vimy Ridge

In April, 1917 during World War 1, Canadian forces fought above ground to beat the Germans and force them to surrender their position on Vimy Ridge - France. Underground however, New Zealand combat engineers dug tunnels and blew up the Germans from below ground. One day during that month a young Maori soldier is 'loaned' to the Canadian infantry to supplement their ranks for a night patrol and goes missing.
When his uncle (also a New Zealand soldier) finds out about this, he goes AWOL to search for his nephew but is captured by the Germans instead.