When they met at a motorcycle club in 1912, Elsie Knocker was a 30-year-old motorcycling divorcee dressed in bottle-green Dunhill leathers, and Mairi Chisholm was a brilliant 18-year old mechanic, living at home and borrowing tools from her brother. Little did they know that theirs was to become one of the most extraordinary stories of the First World War.

In 1914, they roared off to London 'to do their bit', and within a month they were in 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, visited by journalists and photographers as well as royals and VIPs. Glamorous and influential, they were having the time of their lives, and for four years, Elsie and Mairi stayed in Pervyse, until they were nearly killed by arsenic gas in the spring of 1918. But returning home and adjusting to peacetime life was to prove even more challenging than the war itself.