main character is wearing a gas mask during an assault on German soldiers in WWI - as are others, that goes bad when the wind shifts, and a nerve gas that causes complete insanity and psychopathic behavior fall on their own troops with faulty gas masks. Was initially made to cause disorder among the German ranks.

initially, it starts off as bad decision making, orders not being followed. Getting lost. Different phases of the gas. Troops discover that their gas masks leak. Men fire on each other, bombard own troops. Surgeons preform unnecessary surgeries.  People see things that don't exist. They group up against others - tie them up, punish them, execute etc. Eventually, men affected kill one another, mutilate themselves, think they are animals etc, eat human flesh. Until they die.

PHASES OF GAS ATTACK

Phase 1: Mania. Nervous restlessness. Phase 2: Hyper awareness, mild neurosis. Phase 3: impaired decision making, thought disorder. strong neurosis - obsessive compulsive, pyromania, phobic avoidance, lethargy, disturbing thoughts. God complex. Irresistible impulses, abusive behavior Phase 4. psychopathic behavior 1  Superficial charm and average intelligence. 2  Absence of delusions and other signs of irrational thinking. 3  Absence of nervousness or neurotic manifestations. 4  Unreliability. 5  Untruthfulness and insincerity. 6  Lack of remorse or shame. 7  Antisocial behavior without apparent compunction. 8  Poor judgement and failure to learn from experience. 9  Pathological egocentricity and incapacity to love. 10  General poverty in major affective reactions. 11  Specific loss of insight. 12  Unresponsiveness in general interpersonal relations. 13  Fantastic and uninviting behavior with drink, and sometimes without. 14  Suicide threats rarely carried out. 15  Sex life impersonal, trivial, and poorly integrated. Phase 5: hypnagogic or hypnopompic hallucinations, where unusual sensory experiences or thoughts appear during waking or drifting off to sleep. Elimination of Ego/ ID, peacefulness. Phase 6: Paranoid delusions, primary and secondary, monothematic delusions: capgrass (friends, spouse objects replaced by something, something else) ▪  Capgras delusion is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor. ▪  Fregoli delusion is the belief that various people that the believer meets are actually the same person in disguise. ▪  Intermetamorphosis is the belief that people in the environment swap identities with each other whilst maintaining the same appearance. ▪  Subjective doubles, in which a person believes there is a doppelganger or double of him or herself carrying out independent actions. ▪  Cotard delusion is the belief that oneself is dead or does not exist; sometimes coupled with the belief that they are putrifying or missing their internal organs. ▪  Mirrored self-misidentification is the belief that one's reflection in a mirror is some other person. ▪  Reduplicative paramnesia is the belief that a familiar person, place, object or body part has been duplicated. For example, a person may believe that they are in fact not in the hospital to which they were admitted, but an identical-looking hospital in a different part of the country. ▪  Unilateral neglect is the delusion where one denies ownership of a limb or an entire side of ones body (often connected with stroke). ▪  delusions of alien control are delusions that someone or something else is controlling ones actions. ▪  thought insertion is the delusion that someone else is putting words or thoughts in one's brain. Phase 7: violent behavior against others Phase 8: Complete insanity, no rational behaviors. Extreme violent behavior. Phase 9: Cannibalism, blood lust. mutilation. Clinical Lycanthropy, thoughts of being changed into an animal etc. Catatonia, corporealism, blindness, loss of senses. Phase 10: Death.

Possible scenario is that main character is affected, may be an antidote. Follow multiple men as they run around delusional. For instance, one man finds himself calling himself and finds that he is in a shell hole drowning in mud, he then suffocates  man and himself.  Someone sees "Angel of Death," perhaps woman with wings on horseback in noman's land.

One man survives, executed by Generals who will not admit their mistake.