The script is based on the French novel La mort est mon métier by Robert Merle, which was published in 1952 (English edition: Death Is My Trade).
Like the novel, the film is partly based on interrogation records of the trial against Rudolf Höß, SS-officer and commander of the Nazi concentration and extermination camp Auschwitz, as well as on his autobiographical notes.
The real Rudolf Höß had gone into hiding allegedly working as a boatman after World War II using this (fake) name until he was unmasked and arrested in 1946.
The film is divided into 14 different episodes, which describe fragmentary and important scenes of Franz Lang's (alias Rudolf Höss) life.
Severely wounded and carrying his machine gun, Franz Lang drags himself behind the front line, where he is found unconscious by Captain Günther.
As a result, he joins the extreme right-wing Freikorps Roßbach [de ], which intervenes in the Ruhr Uprising against left-wing revolutionary workers in the Baltic states and on other occasions.
But before he can shoot himself with his Mauser pistol, one of his fellow construction workers visits him: He instantly guesses what Lang is about to do and warns him to stay loyal to Germany and that he is burdened with the responsibility for this country, even though he may no longer be a soldier.
In 1922 Franz Lang visits a (Sturmlokal) belonging to the local SA: He tells the SA-Obersturmführer that he wants to have responsibility and help Germany rise to power again.
As a member of the NSDAP and SA, Franz Lang responds to a call for a group of soldiers from a couple of landowners who want their land protected.
The free corps members present at the meeting abduct and beat up the alleged traitor in a forest and Franz Lang shoots him.
One frightened person involved in the murder reveals the crime to the authorities and in 1924 Franz Lang is sentenced to ten years in prison.
Even though he and his wife would prefer to carry on working in agriculture, Lang accepts the offer as a "commitment to the party and the homeland" which Himmler approves.
More or less incidentally, Lang develops the idea of using the poison cyclone B as a "hygienically clean" and "effective" solution to gas the Jews who are deported to Auschwitz.