In the First World War, men on horseback with swords fight against an emerging modern weapon, the machine gun. In Northern France, on the site of a cavalry charge into the face of relentless machine gun fire, the Trench Detectives discover evidence of a desperate act of bravery that stopped the German advance in the Spring of 1918, but decimated the ranks of a Canadian cavalry unit. It was the last great cavalry charge of the First World War, and it was made by Canadian soldiers.