The story is told in five acts. In 1915, German troops led by Captain von Epstein capture the peaceful town of Loos and start committing atrocities on the local population. Von Epstein lusts after a young peasant girl, Émilienne Moreau (Jane King), but she escapes to the Allied lines. Inspired by the vision of Joan of Arc (Jean Robertson), she helps encourage the Allied troops in an attack to retake the town. She falls for a French dispatch rider (Clive Farnham) who is captured by the Germans and takes part in shooting German officers who are sniping on the Red Cross. Emilienne manages to engineer her lover's escape and winds up married to them. She is also awarded a military cross.
The story is told in four parts. The film starts at the English home of Edith Cavell before the war, then jumps forward six years to a Belgium hospital, where Cavell is working. The war is about to start and Dr Schultz suggests Nurse Cavell return home but she refuses, saying her place is with the sick. She gets an invitation to the wedding of two friends, Lt Renard and Yvonne Loudet. Herr Cries is also invited; he pretends to be a medical student but is in fact a foreign spy and is a rejected suitor of Yvonne. He forces himself on her but Lt Renard knocks him out and Cries departs, swearing vengeance. The wedding ends when everyone gets news that war has been declared and Renard goes to military headquarters.
The Gavins claimed the plot "followed closely the facts contained in the official report of the British Admiralty" about the Fryatt incident, with a Belgian love story added. The film begins after Fryatt, the commander of a merchant ship, has rammed a German submarine, and has returned to London a hero. German spies seek to track him down. Fryatt goes on another voyage, is captured by the Germans and executed.