The incredible story of two courageous and spirited women who were the only female participants to serve on the Western Front during World War I   When they met at a motorcycle club in 1912, Elsie Knocker was a thirty year-old motorcycling divorcee dressed in bottle-green Dunhill leathers, and Mairi Chisholm was a brilliant eighteen-year old mechanic. Little did they know that theirs was to become one of the most extraordinary stories of World War I.   In 1914, they roared off into the thick of things in Belgium, driving ambulances to distant military hospitals. Frustrated by the number of men dying of shock in the back of their vehicles, they set up their own first-aid post on the front line in the village of Pervyse, near Ypres, risking their lives working under sniper fire and heavy bombardment for months at a time.   As news of their courage and expertise spread, the "Angels of Pervyse" became celebrities, but returning home and adjusting to peacetime life was to prove more challenging than even the war itself.