The film opens when the British Army finds itself overwhelmed by massive casualties. Major Munro, a physician attached to the Royal Army Medical Corps (RAMC), decides to organize a volunteer Flying Ambulance Corps. He recruits four women: Elsie Knocker (British), Mairi Chisholm (Scottish), Dorothy Fielding (Canadian) and Helen Gleason (American). The women are sent to a field hospital in Furnes, Flanders. But before long, Elsie discovers that many wounded soldiers die of shock during the transport from the trenches to the hospital. She implores Dr. Munro to move the field hospital closer to the front. When he declines, the four women steal an ambulance, packed with supplies, and begin to operate their own dressing station -- in an abandoned village called Pervyse, a stone's throw away from the trenches. Pervyse is just north of the Ypres 'Salient,' a dangerous bulge in the German lines which actually exposes the Allied soldiers to German artillery from three sides...