The film is about a WW1 soldier Jean Diaz who fights at Verdun but survives the war and promises his fallen comrades that he will work after the war has ended to make sure there are no more wars. He becomes a scientist in the glass making industry and develops a formula for making glass which is as strong as steel which he hopes will make war less likely because of its defensive possibilities. His design is stolen by the company which wants to use it in the growing arms race against the other European powers in the late 1930s. In disgust and anger Diaz returns to Verdun to be close to his fallen comrades. Through a process not well explained in the film, he finds a map of the underground tombs and ossuaries (repositories of the bones of unidentified soldiers) at the Verdun memorial where nearly 700,000 men died and finds a way to communicate with the dead. He is driven made by the experience but when he hears that the European powers powers have mobilized for another war he snaps out of his madness and proceeds to summon all his dead comrades from the grave. The film ends with all the dead soldiers of WW1 rising up from their graves to march in protest at the continuing war-mongering by the politicians and war manufacturers. It has quite remarkable special effects for the time with endless columns of dead soldiers marching or rather staggering about calling out to their comrades. The scenes where the statues of the fallen soldiers gradually turn into walking corpses are remarkable.
I have split an extract of the last 22 minutues of the film into 3 smaller clips: